Describing Motion Flashcards

All 34 cards in this deck

What is a scalar quantity?

A quantity that has magnitude (size) but no specific direction.

What is a vector quantity?

A quantity that has both magnitude (size) and a specific direction.

Name four scalar quantities.

Distance, speed, mass and energy.

Name four vector quantities.

Displacement, velocity, acceleration and force (weight and momentum are also vectors).

State the equation linking average speed, distance and time.

average speed (m/s) = distance (m) ÷ time (s)

What is a typical walking speed?

About 1.5 m/s.

What is a typical cycling speed?

About 6 m/s.

What is a typical speed of a car?

About 25 m/s.
e.g. roughly 13 m/s in a town, 30 m/s on a motorway.

What is the typical speed of sound in air?

About 330 m/s.

What is a typical wind speed?

About 5–20 m/s, depending on the weather.

What is velocity?

Speed in a stated direction.

True or false? An object moving at constant speed always has constant velocity.

False. If its direction changes, its velocity changes even though the speed stays the same.

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

The speed of the object.

What does a horizontal line on a distance–time graph show?

The object is stationary (not moving).

True or false? A straight sloping line on a distance–time graph shows an object that is accelerating.

False. A straight sloping line shows constant speed; a curved line shows changing speed.

What is acceleration?

The rate of change of velocity, i.e. how quickly an object's velocity changes. Its unit is m/s².

What is the acceleration of an object travelling at constant velocity?

Zero.

What is the value of the acceleration in free fall, g, near the Earth's surface?

10 m/s².

State the equation linking acceleration, change in velocity and time taken.

acceleration (m/s²) = change in velocity (m/s) ÷ time taken (s), i.e. $a = (v - u) \div t$

State the equation linking final velocity, initial velocity, acceleration and distance.

$v^2 - u^2 = 2 \times a \times x$, where $v$ and $u$ are in m/s, $a$ in m/s² and $x$ in m

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

The acceleration of the object.

True or false? A horizontal line on a velocity–time graph shows that the object is stationary.

False. It shows constant velocity (zero acceleration); the object may still be moving.

On a velocity–time graph, how is an object whose acceleration is decreasing shown?

As a curve of decreasing gradient (still rising, but less steeply).

What does the area between the line and the time axis on a velocity–time graph represent?

The distance travelled.

What is the formula for the area of a trapezium, used for the area under a velocity–time graph?

$\frac{1}{2} \times$ (sum of the two parallel sides) $\times$ width.

What are the steps in a laboratory method for finding the speed of an object?
e.g. a toy car at the bottom of a slope

1. Measure a relevant distance (e.g. along the bench)
2. Measure the time taken for that distance (stopwatch or light gate)
3. Use speed = distance ÷ time, repeating and averaging

How does a light gate measure the speed of a moving object?

It times how long a card on the object blocks the beam; speed = length of card ÷ time.

Why does a light gate or electronic timer give a more accurate speed than a hand-held stopwatch?

It eliminates (human) reaction time.

Apart from using an electronic timer, give two ways to improve a stopwatch method for timing a falling ball.

Increase the drop height to reduce the effect of reaction time; repeat the measurement and average.

True or false? On a velocity–time graph, a steeper line means the object is moving faster.

False. A steeper line means a greater acceleration; the speed is read from the height of the line.

What is a typical running speed?

About 3 m/s.

What is displacement?

How far an object ends up from where it started, measured in a straight line, together with the direction of that change in position.

What is a deceleration?

An acceleration with a negative value: the object is slowing down, so its change in velocity is negative.

How do you find the speed at one particular time from a curved distance–time graph?

Draw a straight line that just touches the curve at that time (a tangent); the speed equals the gradient of that line.