True or False? When drawing free-body force diagrams, objects can be represented as point particles placed at the object's centre of mass.

True. When drawing free-body force diagrams, objects are represented as point particles placed at the object's centre of mass.

True or False? Free-body force diagrams show forces acting on multiple objects or systems.

False. Free-body force diagrams show multiple forces acting on one object or one system .

State two quantities that a force arrow represents.

The two quantities that a force arrow represents are: the magnitude of the force the direction of the force

Define the term resultant force .

A resultant force is the vector sum of all the forces exerted on an object, which describes the combined action of all the forces.

True or False? When forces are balanced, they produce a non-zero resultant force.

False. When forces are balanced, they produce a resultant force of zero .

When two forces in different planes act on an object, how can the resultant force be found?

When two forces act on an object in different planes, the resultant force can be found by resolving vectors. This can be done by using: Pythagoras' theorem trigonometry vector diagrams (triangle or quadrilateral method)

True or False? An object moving at a constant velocity has no resultant force acting on it.

True. An object moving at a constant velocity has no resultant force acting on it.

Define Newton's first law of motion.

Newton's first law of motion states that a body will remain at rest or move with constant velocity unless acted on by a resultant force.

True or False? According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by a resultant force.

True. According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by a resultant force.

Define the term translational equilibrium .

An object is in translational equilibrium if the vector sum of all the forces acting on it are zero, and therefore there is no resultant force .

According to Newton's first law, what would happen to a body that is travelling at a constant velocity if no resultant force acted on it?

According to Newton's first law, a body travelling at a constant velocity would remain travelling at that constant velocity if no resultant force acted upon it. There would be no change in the object's motion.

What are the three ways that a resultant force can change an object's motion?

The three ways that a resultant force can change an object's motion are: speed it up (accelerate) slow it down (decelerate) change its direction

A resultant force acts in the direction of motion of an object. Describe the change in the object's motion.

If a resultant force acts in the direction of motion of an object, then the object will speed up / accelerate in the direction of motion.

A resultant force opposes the direction of motion of an object. Describe the change in the object's motion.

If a resultant force opposes the direction of motion of an object, then the object will slow down / decelerate.

A resultant force acts at an angle to the direction of motion of an object. Describe the change in the object's motion.

If a resultant force acts at an angle to the direction of motion of an object, then the object will change direction .

True or False? Acceleration always acts in the same direction as the resultant force.

True. Acceleration does always act in the same direction as the resultant force.

True or False? If no drag forces are present, then the acceleration of a falling object is independent of its mass.

True. If no drag forces are present, then the acceleration of a falling object is independent of its mass. Astronauts on the Moon dropped a feather and a hammer from equal heights and found that they landed at the same time.

State Newton's second law of motion in terms of momentum .

Newton's second law , in terms of momentum , states that the resultant force on an object is equal to its rate of change of momentum.

True or False? Newton's first and second laws of motion can involve multiple forces acting on one object.

True. Newton's first and second laws of motion can involve multiple forces acting on one object.

True or False? Newton's third law of motion involves two objects exerting the same type of force on each other.

True. Newton's third law of motion involves two objects exerting the same type of force on each other.

State Newton's third law of motion .

Newton's third law states that if one body (Object A) exerts a force on another body (Object B), the second body (Object B) will exert a force on the fist body (Object A) which is equal in magnitude but opposite in direction.

Name four characteristics of a Newton's third law force pair.

The four characteristics of a third law force pair are: the same type of force equal in magnitude opposite in direction acting on different objects

True or False? Weight and normal contact force are an example of a third law pair.

False. Weight and normal contact force are not a third law pair because they: are not the same type of force act on the same object

True or False? According to Newton's third law of motion, if two forces are equal in magnitude and opposite in direction, they are a third law force pair.

False. Two forces that are equal in magnitude and opposite in direction are not necessarily a third law force pair. They must also be the same type of force, exerted by two different objects on each other.

A car drives at a constant velocity on a road. Name a third law force pair in this situation.

Two examples of third law force pairs for a car driving at a constant velocity on a road are: normal contact forces due to the car pushing on the road and the road pushing back on the car weight due to the gravitational pull of the Earth on the car and the gravitational pull of the car on the Earth

Define the term contact force .

A contact force is defined as a force that acts between objects that are physically touching.

Give one example of a contact force.

Examples of contact forces are: surface friction fluid resistance / viscous drag tension normal reaction force

What is surface friction ?

Surface friction is a force that opposes the motion of an object moving over a solid surface.

What is viscous drag ?

Viscous drag is a type of frictional force that occurs when an object moves through a fluid (a liquid or a gas).

Define tension force .

Tension is a force that occurs within an object when a pulling force is applied to both ends.

What is the normal reaction force ?

The normal reaction force is the component of the contact force acting perpendicular to the surface. Reaction forces act on objects supported by a surface.

Define the term fluid in relation to physics.

In physics, a fluid is a liquid or a gas. The particles in a fluid are free to move around.

Define a non-contact force .

A non-contact force is a force which acts at a distance without any physical contact between bodies due to the action of a field.

State one example of a non-contact force.

Examples of non-contact forces are: gravitational force (weight) electrostatic force magnetic force

What is the gravitational force ?

The gravitational force, or weight, is the attractive force experienced by two objects with mass in a gravitational field.

What is the electrostatic force ?

The electrostatic force is an attractive or repulsive force experienced by charged objects in an electric field.

What is the magnetic force ?

The magnetic force is an attractive or repulsive force experienced between magnetic poles in a magnetic field.

True or False? Air resistance is a non-contact force.

False. Air resistance is a type of fluid resistance or viscous drag caused by collisions with air particles. Therefore, air resistance is a contact force.

True or False? When a frictional force is exerted on an object, energy is transferred.

True. When a frictional force is exerted on an object, energy is transferred.

True or False? When a frictional force is exerted on an object, the temperature of the object decreases.

False. When a frictional force is exerted on an object, the temperature of the object increases because energy is transferred to the object by heating.

What causes surface friction?

Surface friction is caused by imperfections in the surfaces of two objects that rub against one another.

Define the term static friction .

Static friction is a type of surface friction that occurs when an object is stationary on a surface.

Define the term dynamic friction .

Dynamic friction is a type of surface friction that occurs when an object is moving across a surface.

True or False? Surface friction always acts parallel to the plane of contact between the object and the surface.

True. Surface friction always acts parallel to the plane of contact between the object and the surface.

True or False? Static friction decreases in magnitude until movement begins.

False. Static friction increases in magnitude until movement begins.

True or False? For any given situation, static friction will reach a maximum value that is larger than that of dynamic friction.

True. For any given situation, static friction will reach a maximum value that is larger than that of dynamic friction.

True or False? For a constant pushing force, dynamic friction will be constant.

True. For a constant pushing force, dynamic friction will be constant . This is known as the coefficient of dynamic friction.

A material obeys Hooke’s law if the extension of the material is directly proportional to the applied force up to the limit of proportionality.

Define the term spring constant .

The spring constant is a property of the material being stretched and describes the stiffness of the material.

True or False? The stiffer the spring, the smaller the spring constant.

False. The stiffer the spring, the greater the spring constant.

True or False? Hooke's law applies to extensions and compressions.

True. Hooke's law does apply to extensions and compressions.

IBPhysicsDPHLFlashcardsSpace, Time & MotionForces & Momentum

Forces & Momentum (DP IB Physics)

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1/142

FrontFree-Body Diagrams
True or False?
When drawing free-body force diagrams, objects can be represented as point particles placed at the object's centre of mass.
FrontFree-Body Diagrams
State two quantities that a force arrow represents.
BackFree-Body Diagrams
The two quantities that a force arrow represents are:
the magnitude of the force
the direction of the force

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Cards in this collection (142)

True or False?
When drawing free-body force diagrams, objects can be represented as point particles placed at the object's centre of mass.
True.
When drawing free-body force diagrams, objects are represented as point particles placed at the object's centre of mass.
True or False?
Free-body force diagrams show forces acting on multiple objects or systems.
False.
Free-body force diagrams show multiple forces acting on one object or one system.
State two quantities that a force arrow represents.
The two quantities that a force arrow represents are:
- the magnitude of the force
- the direction of the force
Define the term resultant force.
A resultant force is the vector sum of all the forces exerted on an object, which describes the combined action of all the forces.
True or False?
When forces are balanced, they produce a non-zero resultant force.
False.
When forces are balanced, they produce a resultant force of zero.
When two forces in different planes act on an object, how can the resultant force be found?
When two forces act on an object in different planes, the resultant force can be found by resolving vectors.
This can be done by using:
- Pythagoras' theorem
- trigonometry
- vector diagrams (triangle or quadrilateral method)
Draw a free-body force diagram for the object on Earth in this situation.
The free-body force diagram for this situation should look like:
A car accelerates in the positive direction. The thrust force from the engine on the car is 1000 N, the air resistance on the car is 50 N and the friction from the road on the car is 500 N. What is the resultant force on the car?
The thrust force from engine on the car is $1000 N$
The combined frictional forces are $(- 50) + (- 500) = - 550 N$
Therefore, the resultant force is $F = 1000 + - 550 = 450 N$ (in the positive direction).
True or False?
An object moving at a constant velocity has no resultant force acting on it.
True.
An object moving at a constant velocity has no resultant force acting on it.
Define Newton's first law of motion.
Newton's first law of motion states that a body will remain at rest or move with constant velocity unless acted on by a resultant force.
True or False?
According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by a resultant force.
True.
According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by a resultant force.
Define the term translational equilibrium.
An object is in translational equilibrium if the vector sum of all the forces acting on it are zero, and therefore there is no resultant force.
According to Newton's first law, what would happen to a body that is travelling at a constant velocity if no resultant force acted on it?
According to Newton's first law, a body travelling at a constant velocity would remain travelling at that constant velocity if no resultant force acted upon it. There would be no change in the object's motion.
What are the three ways that a resultant force can change an object's motion?
The three ways that a resultant force can change an object's motion are:
- speed it up (accelerate)
- slow it down (decelerate)
- change its direction
Define Newton's second law of motion.
Newton's second law of motion states that the resultant force on an object is directly proportional to its acceleration.
State the equation for Newton's second law of motion.
The equation for Newton's second law of motion is $F = m a$
Where:
- $F$ = force, measured in newtons (N)
- $m$ = mass, measured in kilograms (kg)
- $a$ = acceleration, measured in metres per second squared (m s⁻²).
A resultant force acts in the direction of motion of an object.
Describe the change in the object's motion.
If a resultant force acts in the direction of motion of an object, then the object will speed up / accelerate in the direction of motion.
A resultant force opposes the direction of motion of an object.
Describe the change in the object's motion.
If a resultant force opposes the direction of motion of an object, then the object will slow down / decelerate.
A resultant force acts at an angle to the direction of motion of an object.
Describe the change in the object's motion.
If a resultant force acts at an angle to the direction of motion of an object, then the object will change direction.
True or False?
Acceleration always acts in the same direction as the resultant force.
True.
Acceleration does always act in the same direction as the resultant force.
True or False?
If no drag forces are present, then the acceleration of a falling object is independent of its mass.
True.
If no drag forces are present, then the acceleration of a falling object is independent of its mass. Astronauts on the Moon dropped a feather and a hammer from equal heights and found that they landed at the same time.
State Newton's second law of motion in terms of momentum.
Newton's second law, in terms of momentum, states that the resultant force on an object is equal to its rate of change of momentum.
True or False?
Newton's first and second laws of motion can involve multiple forces acting on one object.
True.
Newton's first and second laws of motion can involve multiple forces acting on one object.
True or False?
Newton's third law of motion involves two objects exerting the same type of force on each other.
True.
Newton's third law of motion involves two objects exerting the same type of force on each other.
State Newton's third law of motion.
Newton's third law states that if one body (Object A) exerts a force on another body (Object B), the second body (Object B) will exert a force on the fist body (Object A) which is equal in magnitude but opposite in direction.
Name four characteristics of a Newton's third law force pair.
The four characteristics of a third law force pair are:
- the same type of force
- equal in magnitude
- opposite in direction
- acting on different objects
True or False?
Weight and normal contact force are an example of a third law pair.
False.
Weight and normal contact force are not a third law pair because they:
- are not the same type of force
- act on the same object
True or False?
According to Newton's third law of motion, if two forces are equal in magnitude and opposite in direction, they are a third law force pair.
False.
Two forces that are equal in magnitude and opposite in direction are not necessarily a third law force pair.
They must also be the same type of force, exerted by two different objects on each other.
A car drives at a constant velocity on a road.
Name a third law force pair in this situation.
Two examples of third law force pairs for a car driving at a constant velocity on a road are:
- normal contact forces due to the car pushing on the road and the road pushing back on the car
- weight due to the gravitational pull of the Earth on the car and the gravitational pull of the car on the Earth
Define the term contact force.
A contact force is defined as a force that acts between objects that are physically touching.
Give one example of a contact force.
Examples of contact forces are:
- surface friction
- fluid resistance / viscous drag
- tension
- normal reaction force
What is surface friction?
Surface friction is a force that opposes the motion of an object moving over a solid surface.
What is viscous drag?
Viscous drag is a type of frictional force that occurs when an object moves through a fluid (a liquid or a gas).
Define tension force.
Tension is a force that occurs within an object when a pulling force is applied to both ends.
What is the normal reaction force?
The normal reaction force is the component of the contact force acting perpendicular to the surface.
Reaction forces act on objects supported by a surface.
Define the term fluid in relation to physics.
In physics, a fluid is a liquid or a gas. The particles in a fluid are free to move around.
Define a non-contact force.
A non-contact force is a force which acts at a distance without any physical contact between bodies due to the action of a field.
State one example of a non-contact force.
Examples of non-contact forces are:
- gravitational force (weight)
- electrostatic force
- magnetic force
What is the gravitational force?
The gravitational force, or weight, is the attractive force experienced by two objects with mass in a gravitational field.
What is the electrostatic force?
The electrostatic force is an attractive or repulsive force experienced by charged objects in an electric field.
What is the magnetic force?
The magnetic force is an attractive or repulsive force experienced between magnetic poles in a magnetic field.
True or False?
Air resistance is a non-contact force.
False.
Air resistance is a type of fluid resistance or viscous drag caused by collisions with air particles. Therefore, air resistance is a contact force.
True or False?
When a frictional force is exerted on an object, energy is transferred.
True.
When a frictional force is exerted on an object, energy is transferred.
True or False?
When a frictional force is exerted on an object, the temperature of the object decreases.
False.
When a frictional force is exerted on an object, the temperature of the object increases because energy is transferred to the object by heating.
What causes surface friction?
Surface friction is caused by imperfections in the surfaces of two objects that rub against one another.
Define the term static friction.
Static friction is a type of surface friction that occurs when an object is stationary on a surface.
Define the term dynamic friction.
Dynamic friction is a type of surface friction that occurs when an object is moving across a surface.
True or False?
Surface friction always acts parallel to the plane of contact between the object and the surface.
True.
Surface friction always acts parallel to the plane of contact between the object and the surface.
True or False?
Static friction decreases in magnitude until movement begins.
False.
Static friction increases in magnitude until movement begins.
True or False?
For any given situation, static friction will reach a maximum value that is larger than that of dynamic friction.
True.
For any given situation, static friction will reach a maximum value that is larger than that of dynamic friction.
True or False?
For a constant pushing force, dynamic friction will be constant.
True.
For a constant pushing force, dynamic friction will be constant. This is known as the coefficient of dynamic friction.
State the equation for static friction.
The equation for static friction is $F_{f} \leq μ_{s} F_{N}$
Where:
- $F_{f}$ = frictional force, measured in newtons (N)
- $μ_{s}$ = coefficient of static friction
- $F_{N}$ = normal reaction force, measured in newtons (N)
State the equation for dynamic friction.
The equation for static friction is $F_{f} = μ_{d} F_{N}$
Where:
- $F_{f}$ = frictional force, measured in newtons (N)
- $μ_{d}$ = coefficient of dynamic friction
- $F_{N}$ = normal reaction force, measured in newtons (N)
State Hooke's law.
A material obeys Hooke’s law if the extension of the material is directly proportional to the applied force up to the limit of proportionality.
State the equation for Hooke's law.
The equation for Hooke's law is $F_{H} = - k x$
Where:
- $F_{H}$ = elastic restoring force, measured in newtons (N)
- $k$ = spring constant, measured in newtons per metre (N m^–1)
- $x$ = extension, measured in metres (m)
Define the term spring constant.
The spring constant is a property of the material being stretched and describes the stiffness of the material.
True or False?
The stiffer the spring, the smaller the spring constant.
False.
The stiffer the spring, the greater the spring constant.
True or False?
Hooke's law applies to extensions and compressions.
True.
Hooke's law does apply to extensions and compressions.
What does the linear portion of a force-extension graph represent?
The linear portion of a force-extension graph shows that the force applied is directly proportional to the extension, and so the material obeys Hooke's law.
What does the gradient of the linear region of a force-extension graph represent?
The gradient of the linear region of a force-extension graph represents the spring constant, $k$ .
What does the gradient of the linear region of an extension-force graph represent?
The gradient of the linear region of an extension-force graph represents $\frac{1}{k}$ .
Where:
- $k$ = spring constant, measured in newtons per metre (N m^–1)
State the equation for Stokes' law.
The equation for Stokes' law is $F_{d} = 6 π η r v$
Where:
- $F_{d}$ = viscous drag force, measured in newtons (N)
- $η$ = fluid viscosity, measured in newton seconds per metres squared (N s m^–2) or pascal seconds (Pa s)
- $r$ = radius of sphere, measured in metres (m)
- $v$ = velocity of sphere through fluid, measured in metres per second (m s^–1)
Define the term viscosity.
The viscosity of a fluid is its resistance to movement.
True or False?
The rate of flow of a fluid is inversely proportional to its coefficient of viscosity.
True.
The rate of flow of a fluid is inversely proportional to its coefficient of viscosity.
True or False?
The magnitude of the viscous drag force is dependent on the speed of the object moving through the fluid.
True.
The magnitude of the viscous drag force is dependent on the speed of the object moving through the fluid.
True or False?
The magnitude of the viscous drag force is independent of the volume of the object moving through the fluid.
False.
The magnitude of the viscous drag force is dependent on the volume of the object moving through the fluid.
True or False?
The magnitude of the viscous drag force is dependent on the shape of the object moving through the fluid.
True.
The magnitude of the viscous drag force is dependent on the shape of the object moving through the fluid.
True or False?
The force of buoyancy is only exerted on objects that are immersed in liquids.
False.
The force of buoyancy is exerted on objects that are immersed in fluids (liquids and gases), not just liquids.
True or False?
The buoyancy force is exerted on a body due to the displacement of the fluid it is immersed in.
True.
The buoyancy force is exerted on a body due to the displacement of the fluid it is immersed in.
State the equation for the buoyancy force.
The equation for the buoyancy force is $F_{b} = ρ V g$
Where:
- $F_{b}$ = buoyancy force, measured in newtons (N)
- $ρ$ = density of fluid, measured in kilograms per cubic metre (kg m^–3)
- $V$ = volume of the fluid displaced, measured in cubic metres (m^–3)
- $g$ = acceleration of free fall, measured in metres per second squared (m s^–2)
State the equation for the weight of a sphere of volume $V$ and density $ρ$ .
The weight of a sphere is $W_{s} = ρ_{s} V_{s} g$
Where:
- $W_{s}$ = weight of sphere, measured in newtons (N)
- $ρ$ = density of sphere, measured in kilograms per cubic metre (kg m^–3)
- $V$ = volume of sphere, measured in cubic metres (m³)
- $g$ = acceleration of free fall, measured in metres per second squared (m s^–2)
True or False?
The terminal velocity of a sphere falling through a fluid is indirectly proportional to the square of the radius of the sphere.
False.
The terminal velocity of a sphere falling through a fluid is directly proportional to the square of the radius of the sphere.
True or False?
The terminal velocity of a sphere falling through a fluid is directly proportional to the viscosity of the fluid.
False.
The terminal velocity of a sphere falling through a fluid is indirectly proportional to the viscosity of the fluid.
Define linear momentum.
Linear momentum is the momentum of an object that is moving in only one dimension.
True or False?
The linear momentum of an object remains constant, unless the system is acted upon by an external resultant force.
True.
The linear momentum of an object does remain constant unless the system is acted upon by an external resultant force.
State the equation for linear momentum.
The equation for linear momentum is $p = m v$
Where:
- $p$ = momentum, measured in kilogram metres per second (kg m s^–1)
- $m$ = mass, measured in kilograms (kg)
- $v$ = velocity, measured in metres per second (m s^–1)
True or False?
Linear momentum is a vector quantity.
True.
Linear momentum is a vector quantity with both magnitude and direction.
State the principle of linear momentum.
The principle of linear momentum states that the total linear momentum before a collision is equal to the total linear momentum after a collision. Unless the system is acted on by a resultant external force.
True or False?
Linear momentum is always conserved.
True.
Linear momentum is always conserved.
A toy car of mass 0.2 kg travels with a velocity of 0.1 m s^–1.
What is the linear momentum of the toy car?
The linear momentum of a toy car of mass 0.2 kg that travels with a velocity of 0.1 m s^–1 is 0.02 kg m s^–1.
- $p = m v$
- $p = 0.2 \times 0.1 = 0.02 kg m s^{- 1}$
Moving object A collides with stationary object B. After the collision, they move in opposite directions.
Write equations for the momentum before and after the collision.
The equations for the momentum before and after a collision between moving object A and stationary object B are:
- $p_{b e f o r e} = m_{A} u_{A} + 0$
- $p_{a f t e r} = - m_{A} v_{A} + m_{B} v_{B}$
Define impulse.
Impulse is when an external resultant force acts on an object for a very short time and changes the object's motion.
What is the symbol for impulse?
The symbol for impulse is $J$ .
State the equation for the impulse of a force.
The equation for the impulse of a force is $J = F ∆ t$
Where:
- $J$ = impulse, measured in newton seconds (N s)
- $F$ = resultant external force applied, measured in newtons (N)
- $∆ t$ = change in time over which the force acts, measured in seconds (s)
True or False?
Impulse is equal to change in momentum.
True.
Impulse is equal to change in momentum. Therefore, change in momentum can be used to indirectly measure impulse.
True or False?
Impulse always acts in the opposite direction to the external resultant force.
False.
Impulse always acts in the same direction as the external resultant force.
True or False?
A larger force exerted for a short time has the same effect as a smaller force exerted for a longer time.
True.
A larger force exerted for a short time has the same effect as a smaller force exerted for a longer time.
True or False?
Increasing the time over which a change in momentum occurs reduces the force applied to the object.
True.
Increasing the time over which a change in momentum occurs reduces the force experienced by the object.
Write an expression for the impulse of the force acting for a time $T$ .
The impulse of the force is $J = \frac{1}{2} F_{m a x} T$ .
Impulse is the area under a force-time graph, therefore:
- $J = (\frac{1}{2} \times F_{m a x} \times \frac{T}{2}) + (\frac{1}{2} \times F_{m a x} \times \frac{T}{2})$
- $J = \frac{1}{2} F_{m a x} T$
True or False?
The equation $F = \frac{∆ p}{∆ t}$ can only be used when mass is constant.
False.
The equation $F = \frac{∆ p}{∆ t}$ can also be used when the mass of the object is not constant.
A toy car collides with a skirting board. The toy car exerts a force of 4.5 N on the skirting board.
State the magnitude and direction of the force exerted by the skirting board on the car.
The force exerted by the skirting board on the car is –4.5 N.
According to Newton's third law:
- the car exerts a force of 4.5 N on the skirting board
- therefore, the skirting board exerts an equal and opposite force of -4.5 N on the car
A student of mass 50 kg sits on a chair.
State the magnitude of the force exerted by the chair on the student.
The magnitude of the force exerted by the chair on the student is 490 N.
The student exerts a normal reaction force on the chair that is equal to the student's weight.
- $W = m g = 50 \times 9.8 = 490 N$
According to Newton's third law, the chair exerts a normal reaction force on the student that is equal in magnitude but opposite in direction.
True or False?
The equation $F = m a$ can be used when mass is not constant.
False.
The equation $F = m a$ can only be used when mass is constant.
How can force, as the rate of change of momentum, be derived from Newton's second law of motion?
Force, as the rate of change of momentum, be derived from Newton's second law of motion as follows:
- $F = m a = \frac{m (v - u)}{t} = \frac{m v - m u}{t} = \frac{∆ p}{∆ t}$
Define the term collision.
A collision is when two or more moving objects come together and exert a force on one another for a relatively short time.
Define the term explosion.
An explosion is when two or more objects that are initially at rest, are propelled apart from one another.
True or False?
Momentum is conserved in all collisions and all explosions.
True.
Momentum is always conserved in collisions and explosions.
True or False?
Kinetic energy is conserved in all collisions and all explosions.
False.
Kinetic energy is only conserved in elastic collisions and explosions.
However, kinetic energy is not conserved if the collision or explosion is inelastic.
Define the term elastic collision.
An elastic collision is a collision in which both the momentum and kinetic energy are conserved.
Define the term inelastic collision.
An inelastic collision is a collision in which the momentum is conserved but the kinetic energy is not.
True or False?
Perfectly elastic collisions only occur between particles.
True.
Perfectly elastic collisions only occur between particles. However, the theoretical idea of an elastic collision can be used in exam questions.
How do you determine if a collision is elastic or inelastic?
To determine whether a collision is elastic or inelastic, compare the kinetic energy before and after the collision. If kinetic energy is conserved, then the collision is elastic.
True or False?
Objects always stick together after an inelastic collision.
False.
A totally inelastic collision is a special case of an inelastic collision where the colliding bodies stick together and move as one body.
Define a radian.
A radian is the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
True or False?
Momentum is conserved in every direction when objects collide.
True.
Momentum is conserved in every direction when objects collide.
What is the angle in radians for a complete circle in terms of $π$ ?
A complete circle is $2 π$ radians.
A moving ball of mass $m_{1}$ collides with a stationary ball of mass $m_{2}$ . After the collision, they move off in different directions.
Write an expression for $v_{1}$ in the vertical ( $y$ ) direction.
An expression for $v_{1}$ in the vertical direction is:
- $v_{1} = \frac{m_{2} v_{2} \sin θ_{2}}{m_{1} \sin θ_{1}}$ or $v_{1} = \frac{0.35 \times 0.48 \times \sin (47)}{0.15 \times \sin (43)}$
State the equation used to convert degrees to radians.
The equation used to convert degrees to radians is $θ rad = θ ° \times \frac{π}{180}$ .
A moving ball of mass $m_{1}$ collides with a stationary ball of mass $m_{2}$ . After the collision, they move off in different directions.
Write an expression for $v_{1}$ in the horizontal ( $x$ ) direction.
An expression for $v_{1}$ in the horizontal direction is
- $v_{1} = \frac{m_{1} u_{1} - m_{2} v_{2} \cos θ_{2}}{m_{1} \cos θ_{1}}$ or $v_{1} = \frac{(0.15 u_{1}) - (0.35 \times 0.48 \times \cos (47))}{0.15 \times \cos (43)}$
What is the angle in radians for a half circle in terms of $π$ ?
A half circle is $π$ radians.
State the equation used to convert radians to degrees.
The equation used to convert radians to degrees is $θ ° = θ rad \times \frac{180}{π}$ .
What is 90° in radians in terms of $π$ ?
90° is $\frac{π}{2}$ radians.
Define angular displacement.
Angular displacement is the change in angle, in radians, of a body as it rotates around a circle.
What is 270° in radians in terms of $π$ ?
270° is $\frac{3 π}{2}$ radians.
Define angular speed.
Angular speed is the change in angular displacement with respect to time.
How is angular speed different to angular velocity?
Angular speed is a scalar quantity, and angular velocity is a vector quantity. Angular speed is the magnitude of angular velocity.
State the equation linking linear speed, and angular speed.
The equation linking linear speed, and angular speed is $v = r ω$
Where:
- $v$ = linear speed, measured in metres per second (m s^–1)
- $r$ = radius of circle, measured in metres (m)
- $ω$ = angular speed, measured in radians per second (rad s^–1)
State the equation linking linear speed, and time period.
The equation linking linear speed, and angular speed is $v = \frac{2 π}{T}$
Where:
- $v$ = linear speed, measured in metres per second (m s^–1)
- $T$ = time period, measured in seconds (s)
An object in circular motion experiences a centripetal force.
Define the term centripetal.
Centripetal means acting toward the centre of the circular path.
True or False?
An object in uniform circular motion travels at a constant speed but with a changing velocity.
True.
An object in uniform circular motion travels at a constant speed but with a changing velocity. Velocity is a vector quantity, so a change in direction is a change in velocity.
Define the term centripetal force.
Centripetal force is defined as the resultant force required to keep a body in a uniform circular motion that acts towards the centre of the circle, perpendicular to the velocity.
State the equation linking centripetal force and linear speed.
The equation linking centripetal force and linear speed is $F = \frac{m v^{2}}{r}$
Where:
- $F$ = centripetal force, measured in newtons (N)
- $m$ = mass, measured in kilograms (kg)
- $v$ = linear speed, measured in metres per second (m s^–1)
- $r$ = radius of orbit, measured in metres (m)
State the equation linking centripetal force and angular speed.
The equation linking centripetal force and linear speed is $F = m r ω^{2}$
Where:
- $F$ = centripetal force, measured in newtons (N)
- $m$ = mass, measured in kilograms (kg)
- $r$ = radius of orbit, measured in metres (m)
- $ω$ = angular speed, measured in radians per second (rad s^–1)
True or False?
The direction of the centripetal force is the same direction as the acceleration.
True.
The direction of the centripetal force is the same direction as the acceleration. Centripetal force is a resultant force. Acceleration always occurs in the direction of the resultant force.
State the centripetal force for the Earth orbiting the Sun.
The centripetal force for the Earth orbiting the Sun is the gravitational force.
State the centripetal force for a ball on a rope moving in a circle.
The centripetal force for a ball on a rope moving in a circle is tension.
State the centripetal force for a car going around a circular track.
The centripetal force for a car going around a circular track is friction.
True or False?
For an object in circular motion, there is no work done.
True.
For an object in circular motion, there is no work done because there is no change in kinetic energy.
State the equation linking centripetal acceleration and linear speed.
The equation linking centripetal acceleration and linear speed is $a = \frac{v^{2}}{r}$
Where:
- $a$ = centripetal acceleration, measured in metres per second squared (m s^–2)
- $v$ = linear speed, measured in metres per second (m s^–1)
- $r$ = radius of circular orbit, measured in metres (m)
Define centripetal acceleration.
Centripetal acceleration is the acceleration of an object towards the centre of a circle when an object is in circular motion at a constant speed.
State the equation linking centripetal acceleration and angular speed.
The equation linking centripetal acceleration and linear speed is $a = ω^{2} r$
Where:
- $a$ = centripetal acceleration, measured in metres per second squared (m s^–2)
- $ω$ = angular speed, measured in radians per second (rad s^–1)
- $r$ = radius of circular orbit, measured in metres (m)
True or False?
Centripetal acceleration is in the same direction as the centripetal force.
True.
Centripetal acceleration is in the same direction as the centripetal force. Centripetal force is a resultant force, acceleration always acts in the same direction as the resultant force.
State the equation linking centripetal acceleration and time period.
The equation linking centripetal acceleration and time period is $a = {(\frac{2 π}{T})}^{2} r = \frac{4 π^{2} r}{T^{2}}$
Where:
- $a$ = centripetal acceleration, measured in metres per second squared (m s^–2)
- $r$ = radius of circular orbit, measured in metres (m)
- $T$ = time period, measured in seconds (s)
Define non-uniform circular motion.
Non-uniform circular motion occurs when there is a changing resultant force on an object in circular motion, such as when an object moves in a vertical circle.
State one example of an object in non-uniform circular motion.
Examples of objects in non-uniform circular motion are:
- a ball swinging on a string in a vertical circle
- swinging a bucket of water in a vertical circle
True or False?
For a ball on a string swinging in a vertical circle, the tension force of the string on the ball is greater at the top of the circle than at the bottom.
False.
For a ball on a string swinging in a vertical circle, the tension force of the string on the ball is greater at the bottom of the circle than at the top. This is because the tension has to overcome the weight force at the bottom of the circle.
True or False?
For a ball on a string swinging in a vertical circle, the direction of the tension force will change continually.
True.
For a ball on a string swinging in a vertical circle, the direction of the tension force will change continually. This is because tension is the centripetal force and is always directed to the centre of the circle.
True or False?
For a ball on a string swinging in a vertical circle, the magnitude of the tension force will be constant.
False.
For a ball on a string swinging in a vertical circle, the magnitude of the tension force will change continuously. This is because tension is the centripetal force, which is greater at the bottom because it also has to overcome the weight force at the bottom of the circle.
For an object in non-uniform circular motion, when in the circle is the centripetal force at a maximum and a minimum?
For an object in non-uniform circular motion, the centripetal force is at a maximum at the bottom of the circle and a minimum at the top of the circle.
State the equation for the centripetal force on a ball swinging in a vertical circle when the ball is at the top of the circle.
The equation for the centripetal force on a ball swinging in a vertical circle when the ball is at the top of the circle is $F = \frac{m v^{2}}{r} + m g$
Where:
- $F$ = centripetal force / tension measured in newtons (N)
- $m$ = mass, measured in kilograms (kg)
- $v$ = velocity, measured in metres per second (m s^–1)
- $r$ = radius of orbit, measured in metres (m)
- $g$ = gravitational field strength, measured in newtons per kilogram (N kg^–1)
State the equation for the centripetal force on a ball swinging in a vertical circle when the ball is at the bottom of the circle.
The equation for the centripetal force on a ball swinging in a vertical circle when the ball is at the bottom of the circle is $F = \frac{m v^{2}}{r} - m g$
Where:
- $F$ = centripetal force / tension, measured in newtons (N)
- $m$ = mass, measured in kilograms (kg)
- $v$ = velocity, measured in metres per second (m s^–1)
- $r$ = radius or orbit, measured in metres (m)
- $g$ = gravitational field strength, measured in newtons per kilogram (N kg^–1)
True or False?
For a ball on a string swinging in a vertical circle, the speed of the ball will be slower at the bottom of the circle than at the top.
False.
For a ball on a string swinging in a vertical circle, the speed of the ball will be faster at the bottom of the circle than at the top, because the acceleration is greater at the bottom.