Define the newton (N) .

The newton is the force that gives a mass of 1 kg an acceleration of 1 m s -2 .

The resultant force on a body is the .......... sum of all the forces acting on it.

The resultant force on a body is the vector sum of all the forces acting on it.

If drag forces are ignored, how does the acceleration of a falling object depend on its mass?

The acceleration is independent of mass — all objects fall with the same acceleration in the absence of drag.

What sign does the acceleration have if the resultant force acts opposite to the direction of motion?

Negative — the object decelerates.

True or False? A heavier object falls with a greater acceleration than a lighter object, if air resistance is ignored.

False. With no drag forces, acceleration is independent of mass — a hammer and a feather dropped on the Moon land at the same time.

Weight is the force on an object due to the pull of gravity (the effect of a gravitational field on a mass); it is a vector quantity measured in newtons .

What is the value of g on Earth, and what are its units?

9.81 m s -2 (equivalently, N kg -1 )

An object's .......... always stays the same, but its weight depends on the strength of the gravitational field it is in.

An object's mass always stays the same, but its weight depends on the strength of the gravitational field it is in.

Why is an object's weight on the Moon about six times less than on Earth, even though its mass is unchanged?

The Moon's gravitational field strength ( 1.63 N kg -1 ) is much lower than Earth's ( 9.81 N kg -1 ), and weight depends on g , not just mass.

True or False? Mass and weight are the same quantity.

False. Mass is a scalar amount of matter in an object; weight is a vector force due to gravity, and varies with gravitational field strength.

Tension is the force experienced by a cable, rope or string when it is pulled, hung, rotated or supported; it always acts away from the mass.

Define normal contact force .

The force arising when an object rests against another, acting at 90° to the plane of contact (also called the reaction force ); it arises from Newton's third law .

The upward buoyancy force acting on an object when it is in a fluid (liquid or gas).

The force that arises when two surfaces are in contact with each other; it always opposes the motion.

What is a free-body diagram used to show?

The forces acting on an object, each represented as a vector arrow scaled to magnitude, pointing in the direction of the force, and labelled with its name.

On a free-body diagram, each arrow is scaled to the .......... of the force it represents.

On a free-body diagram, each arrow is scaled to the magnitude of the force it represents.

True or False? The normal contact force always acts parallel to the surface of contact.

False. The normal contact force always acts perpendicular (at 90°) to the plane of contact.

Define one-dimensional motion .

Motion in just one plane , e.g. purely up and down, or purely left and right.

Define two-dimensional motion .

Motion involving both up and down and left and right, e.g. an object moving on a slope.

On a slope, forces are usually resolved into which two directions, rather than horizontal and vertical?

Parallel and perpendicular to the slope.

For an object of weight W on a slope inclined at angle θ, the components of weight are W sin θ parallel to the slope, and W .......... θ perpendicular to the slope.

For an object of weight W on a slope inclined at angle θ, the components of weight are W sin θ parallel to the slope, and W cos θ perpendicular to the slope.

On an inclined slope, what does the normal reaction force R act perpendicular to?

The plane of contact between the object and the slope.

True or False? On a slope, the normal reaction force always acts vertically upwards, directly opposing weight.

False. The normal reaction force acts perpendicular to the slope's surface , not vertically, unless the slope is horizontal.

A drag force opposes the motion of an object moving through a fluid (gas or liquid), e.g. friction and air resistance .

What are the two most significant factors affecting the magnitude of a drag force?

The speed of the object and its cross-sectional area .

Drag forces always act in the .......... direction to the motion of the object.

Drag forces always act in the opposite direction to the motion of the object.

What is lift , and in what direction does it act relative to the fluid flow?

An upward force on an object moving through a fluid, acting perpendicular to the fluid flow (it arises from Newton's third law).

How does air resistance affect the experimental value of g measured for a falling object?

It makes the measured value less than 9.81 m s -2 .

Name three factors, besides speed and cross-sectional area, that affect an object's maximum speed due to air resistance.

Shape , altitude , temperature and humidity .

True or False? Air resistance increases both the range and the maximum height of a projectile.

False. Air resistance decreases the horizontal component of velocity, which reduces both the range and the maximum height.

Define terminal velocity .

The constant velocity reached when the drag force on a falling body equals its weight, so the resultant force (and acceleration) is zero .

Why does the acceleration of a falling body decrease as its speed increases, before it reaches terminal velocity?

The drag force increases with speed , reducing the resultant force and therefore the acceleration ( F = ma ).

Why does a skydiver reach a lower terminal velocity after deploying their parachute?

The parachute greatly increases the drag force , decelerating the skydiver to a lower terminal velocity to reduce the impact on landing.

On a velocity-time graph, the acceleration at any point is equal to the .......... of the graph.

On a velocity-time graph, the acceleration at any point is equal to the gradient of the graph.

True or False? When a skydiver deploys their parachute, they briefly move upwards before falling again.

False. The skydiver decelerates to a lower terminal velocity; they do not move upwards.

Two skydivers of different masses, A (heavier) and B (lighter), want to join up in freefall. Who should jump first, and why?

Skydiver B (lighter) should jump first — they reach a lower terminal velocity sooner , and heavier skydiver A will fall faster and catch up.

Define terminal velocity .

The maximum, constant velocity reached by a falling object, shown on a velocity-time graph as the point where the line plateaus and has zero gradient.

What are the independent and dependent variables in the terminal velocity investigation?

Independent variable: distance between markers (m) Dependent variable: time to travel between markers (s)

State two control variables in the terminal velocity investigation.

Use the same viscous fluid Use the same ball bearing

Why should the tube used in the terminal velocity investigation be as tall as possible?

It allows the ball bearing to travel at its terminal velocity for longer before reaching the bottom of the tube.

Why should larger intervals be used between the marker bands in this investigation?

It reduces the percentage uncertainty in both the distance and time measurements between the bands.

True or False? A ball bearing falling through a viscous fluid reaches terminal velocity as soon as it enters the liquid.

False. The ball bearing initially accelerates under a resultant downward force; terminal velocity is only reached once the velocity-time graph plateaus .

A LevelPhysicsOCRFlashcards3. Forces & MotionDynamics

Dynamics (OCR A Level Physics): Flashcards

Exam code: H556

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FrontForce & Acceleration
Define the newton (N).

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Cards in this collection (48)

Define the newton (N).
The newton is the force that gives a mass of 1 kg an acceleration of 1 m s^-2.
State Newton's second law relating resultant force, mass and acceleration.
$F = m a$
What is the SI base unit of force?
kg m s^-2
The resultant force on a body is the .......... sum of all the forces acting on it.
The resultant force on a body is the vector sum of all the forces acting on it.
If drag forces are ignored, how does the acceleration of a falling object depend on its mass?
The acceleration is independent of mass — all objects fall with the same acceleration in the absence of drag.
What sign does the acceleration have if the resultant force acts opposite to the direction of motion?
Negative — the object decelerates.
True or False?
A heavier object falls with a greater acceleration than a lighter object, if air resistance is ignored.
False.
With no drag forces, acceleration is independent of mass — a hammer and a feather dropped on the Moon land at the same time.
Define weight.
Weight is the force on an object due to the pull of gravity (the effect of a gravitational field on a mass); it is a vector quantity measured in newtons.
State the equation linking weight, mass and gravitational field strength.
$W = m g$
What is the value of g on Earth, and what are its units?
9.81 m s^-2 (equivalently, N kg^-1)
An object's .......... always stays the same, but its weight depends on the strength of the gravitational field it is in.
An object's mass always stays the same, but its weight depends on the strength of the gravitational field it is in.
Why is an object's weight on the Moon about six times less than on Earth, even though its mass is unchanged?
The Moon's gravitational field strength (1.63 N kg^-1) is much lower than Earth's (9.81 N kg^-1), and weight depends on g, not just mass.
True or False?
Mass and weight are the same quantity.
False.
Mass is a scalar amount of matter in an object; weight is a vector force due to gravity, and varies with gravitational field strength.
Define tension.
Tension is the force experienced by a cable, rope or string when it is pulled, hung, rotated or supported; it always acts away from the mass.
Define normal contact force.
The force arising when an object rests against another, acting at 90° to the plane of contact (also called the reaction force); it arises from Newton's third law.
Define upthrust.
The upward buoyancy force acting on an object when it is in a fluid (liquid or gas).
Define friction.
The force that arises when two surfaces are in contact with each other; it always opposes the motion.
What is a free-body diagram used to show?
The forces acting on an object, each represented as a vector arrow scaled to magnitude, pointing in the direction of the force, and labelled with its name.
On a free-body diagram, each arrow is scaled to the .......... of the force it represents.
On a free-body diagram, each arrow is scaled to the magnitude of the force it represents.
True or False?
The normal contact force always acts parallel to the surface of contact.
False.
The normal contact force always acts perpendicular (at 90°) to the plane of contact.
Define one-dimensional motion.
Motion in just one plane, e.g. purely up and down, or purely left and right.
Define two-dimensional motion.
Motion involving both up and down and left and right, e.g. an object moving on a slope.
On a slope, forces are usually resolved into which two directions, rather than horizontal and vertical?
Parallel and perpendicular to the slope.
For an object of weight W on a slope inclined at angle θ, the components of weight are W sin θ parallel to the slope, and W .......... θ perpendicular to the slope.
For an object of weight W on a slope inclined at angle θ, the components of weight are W sin θ parallel to the slope, and W cos θ perpendicular to the slope.
On an inclined slope, what does the normal reaction force R act perpendicular to?
The plane of contact between the object and the slope.
For an object sliding down a frictionless slope inclined at angle θ, what is its acceleration in terms of g and θ?
$a = g \sin θ$
True or False?
On a slope, the normal reaction force always acts vertically upwards, directly opposing weight.
False.
The normal reaction force acts perpendicular to the slope's surface, not vertically, unless the slope is horizontal.
Define drag force.
A drag force opposes the motion of an object moving through a fluid (gas or liquid), e.g. friction and air resistance.
What are the two most significant factors affecting the magnitude of a drag force?
The speed of the object and its cross-sectional area.
Drag forces always act in the .......... direction to the motion of the object.
Drag forces always act in the opposite direction to the motion of the object.
What is lift, and in what direction does it act relative to the fluid flow?
An upward force on an object moving through a fluid, acting perpendicular to the fluid flow (it arises from Newton's third law).
How does air resistance affect the experimental value of g measured for a falling object?
It makes the measured value less than 9.81 m s^-2.
Name three factors, besides speed and cross-sectional area, that affect an object's maximum speed due to air resistance.
Shape, altitude, temperature and humidity.
True or False?
Air resistance increases both the range and the maximum height of a projectile.
False.
Air resistance decreases the horizontal component of velocity, which reduces both the range and the maximum height.
Define terminal velocity.
The constant velocity reached when the drag force on a falling body equals its weight, so the resultant force (and acceleration) is zero.
Why does the acceleration of a falling body decrease as its speed increases, before it reaches terminal velocity?
The drag force increases with speed, reducing the resultant force and therefore the acceleration (F = ma).
Why does a skydiver reach a lower terminal velocity after deploying their parachute?
The parachute greatly increases the drag force, decelerating the skydiver to a lower terminal velocity to reduce the impact on landing.
On a velocity-time graph, the acceleration at any point is equal to the .......... of the graph.
On a velocity-time graph, the acceleration at any point is equal to the gradient of the graph.
True or False?
When a skydiver deploys their parachute, they briefly move upwards before falling again.
False.
The skydiver decelerates to a lower terminal velocity; they do not move upwards.
Two skydivers of different masses, A (heavier) and B (lighter), want to join up in freefall. Who should jump first, and why?
Skydiver B (lighter) should jump first — they reach a lower terminal velocity sooner, and heavier skydiver A will fall faster and catch up.
Define terminal velocity.
The maximum, constant velocity reached by a falling object, shown on a velocity-time graph as the point where the line plateaus and has zero gradient.
What are the independent and dependent variables in the terminal velocity investigation?
Independent variable: distance between markers (m)
Dependent variable: time to travel between markers (s)
State two control variables in the terminal velocity investigation.
- Use the same viscous fluid
- Use the same ball bearing
Using a more .......... fluid slows the ball bearing down, making it easier to determine its speed accurately.
viscous
Which equation is used to calculate the average velocity of the ball bearing between markers?
speed = distance ÷ time
Why should the tube used in the terminal velocity investigation be as tall as possible?
It allows the ball bearing to travel at its terminal velocity for longer before reaching the bottom of the tube.
Why should larger intervals be used between the marker bands in this investigation?
It reduces the percentage uncertainty in both the distance and time measurements between the bands.
True or False?
A ball bearing falling through a viscous fluid reaches terminal velocity as soon as it enters the liquid.
False.
The ball bearing initially accelerates under a resultant downward force; terminal velocity is only reached once the velocity-time graph plateaus.

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