p9:motion

What is meant by distance and displacement?

• Distance = how far an object moves (scalar).

• Displacement = distance in a given direction (vector).

What is meant by speed and velocity?

• Speed = how fast an object moves (scalar).

• Velocity = speed in a given direction (vector).

What is the unit of speed and velocity?

Metres per second (m/s).

What does a negative velocity mean?

The object is moving in the opposite direction to the positive reference direction.

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

The speed of the object.

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

Draw a tangent at the point and find its gradient.

What does a flat (horizontal) line mean on a distance–time graph?

The object is stationary.

What does a straight, sloping line mean on a distance–time graph

The object is moving at a constant speed.

What does a steeper line mean?

The object is moving faster.

What does the gradient of a velocity–time graph represent?

Acceleration.

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

Distance travelled.

How can you find distance from a velocity–time graph if the graph is curved?

Estimate using counting squares or find the area under the curve.

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

Constant velocity (zero acceleration).

What does a negative gradient represent?

Deceleration (velocity decreasing).

What is the acceleration of free fall on Earth?

pproximately g=9.8 m/s2 downward.

What is meant by terminal velocity?

The constant speed reached when the resistive forces (air resistance) balance the driving force (weight).

Why does a skydiver stop accelerating after some time?

Air resistance increases with speed until it equals the weight → resultant force = 0 → constant velocity (terminal velocity).

What happens to acceleration when resultant force = 0?

Acceleration = 0 m/s²; object moves at constant velocity.

How can you calculate instantaneous velocity from a distance–time graph?

Draw a tangent at the required point; find the gradient of the tangent.

How can you determine acceleration from a velocity–time graph?

Measure the gradient (rise/run) of the graph between two points.

What does the area under the graph between two times represent physically?

The total displacement (with direction) between those times.

On a velocity–time graph, what does a line crossing the time axis mean?

The object changes direction (velocity changes sign).

What kind of motion does a constant, positive gradient represent?

Uniform acceleration in the positive direction.

Typical speed of a person walking, running, and cycling?

• Walking ≈ 1.5 m/s

• Running ≈ 3 m/s

• Cycling ≈ 6 m/s

Typical speed of a car, train, and aircraft?

• Car ≈ 25 m/s

• Train ≈ 50 m/s

• Aircraft ≈ 250 m/s

Why does speed vary for a given person or vehicle?

It depends on terrain, fatigue, wind, traffic, and fuel power.