Forces and Motion (AQA GCSE Physics Triple Paper 2)

What is the difference between scalar and vector quantities?

Scalars have only magnitude (e.g. speed, distance), vectors have magnitude and direction (e.g. velocity, displacement, force).

Define velocity.

Velocity is the speed of an object in a given direction; it is a vector quantity.

What is displacement?

Displacement is the straight-line distance from a starting point to an endpoint in a specific direction.

How can an object be travelling at a constant speed but still be accelerating?

If it's changing direction (e.g. in circular motion), its velocity is changing, so it's accelerating.

Describe what is shown by a distance-time graph with a straight, sloping line.

The object is moving at a constant speed.

What does a flat (horizontal) line on a distance-time graph represent?

The object is stationary.

What does the gradient of a distance-time graph represent?

Speed.

How do you find the speed from a curved distance-time graph?

Draw a tangent at the point and find the gradient of the tangent.

Describe what a straight, sloping line on a velocity-time graph shows.

Constant acceleration or deceleration.

What does the area under a velocity-time graph represent?

Displacement (distance travelled in a direction).

What is acceleration and how is it calculated?

The rate of change of velocity; acceleration = (change in velocity) ÷ time.

What does a flat line on a velocity-time graph mean?

Constant velocity.

What does a negative gradient on a velocity-time graph mean?

The object is decelerating (slowing down).

State Newton’s First Law.

An object will remain at rest or in uniform motion unless acted on by a resultant force.

What is inertia?

The tendency of an object to resist changes in its motion.

State Newton’s Second Law.

The acceleration of an object is directly proportional to the resultant force and inversely proportional to its mass: F = ma.

State Newton’s Third Law.

When two objects interact, they exert equal and opposite forces on each other.

What is the difference between mass and weight?

Mass is the amount of matter in an object (kg); weight is the force acting on it due to gravity (N).

What is terminal velocity and how is it reached?

When the drag force equals the weight, net force = 0, so the object stops accelerating and moves at constant speed.

What factors affect thinking distance?

Reaction time, which is influenced by drugs, tiredness, distractions, and alcohol.

What factors affect braking distance?

Road conditions, weather, tyre/brake condition, mass of vehicle, speed.

What is the typical reaction time for a human?

Between 0.2 and 0.9 seconds.

What is meant by resultant force?

A single force that has the same effect as all the forces acting on an object combined.

How do you calculate the resultant force on an object?

Add forces in the same direction, subtract forces in opposite directions.

What does a free-body diagram show?

All the forces acting on a single object with arrows showing their direction and magnitude.

What is meant by an object being in equilibrium?

All the forces acting on it are balanced; resultant force = 0.

How can you use a force diagram to determine motion?

If the arrows are unbalanced, the object will accelerate in the direction of the larger force.

What is the typical acceleration of free fall on Earth?

Approximately 9.8 m/s².

How do seat belts and airbags protect passengers in a crash?

They increase the time over which momentum changes, reducing the force experienced.

What is the role of crumple zones in cars?

They absorb energy and increase the time taken to stop, reducing the force and injury risk.

What does momentum depend on?

Mass and velocity: momentum = mass × velocity.

What is the law of conservation of momentum?

Total momentum before a collision is equal to total momentum after, provided no external force acts.

In a collision, what causes injuries in terms of forces and motion?

Rapid deceleration leads to large forces acting on the body.

What is stopping distance?

The sum of thinking distance and braking distance.

How does speed affect stopping distance?

Both thinking and braking distance increase with speed; stopping distance increases significantly.

What’s the difference between elastic and inelastic collisions?

In elastic collisions, kinetic energy is conserved; in inelastic, some energy is transferred (e.g. to heat, sound).

What is meant by deceleration and is it a negative acceleration?

Deceleration is a decrease in velocity; yes, it is technically negative acceleration.

How do you estimate the speed of an object from a velocity-time graph?

Use the area under the graph between the time interval.

Why does increasing mass increase momentum?

Because momentum = mass × velocity; if velocity is constant, higher mass means more momentum.

What kind of quantity is force?

A vector quantity—it has both magnitude and direction.

In which direction does friction act?

Opposite to the direction of motion.

What is drag and how does it differ from friction?

Drag is a resistive force through a fluid (air or liquid); friction is usually between solid surfaces.