Describing Motion Flashcards
All 37 cards in this deck
What is a scalar quantity?
A quantity that has only size (magnitude), with no specific direction.
What is a vector quantity?
A quantity that has both size (magnitude) and a specific direction.
Name four vector quantities met in GCSE physics.
Displacement, velocity, acceleration, force (also weight and momentum).
Name four scalar quantities met in GCSE physics.
Distance, speed, mass, energy.
True or false? Energy is a vector quantity.
False. Energy is a scalar — it has size only.
What is velocity?
Speed in a stated direction.
True or false? Speed and velocity are the same quantity.
False. Speed is a scalar; velocity is speed in a stated direction, so it is a vector.
True or false? An object can travel at a constant speed while its velocity changes.
True. If its direction changes, its velocity changes even though its speed is the same.
What is the equation for average speed, and what unit is it measured in?
average speed = distance ÷ time, measured in metres per second (m/s).
What is the equation for the distance travelled, using average speed?
distance travelled (m) = average speed (m/s) × time (s)
What is a typical speed for a person walking?
About 1.5 m/s (about 1 m/s is also accepted).
What is a typical speed for a person running?
About 3 m/s (an Olympic sprinter reaches about 10 m/s).
What is a typical speed for a person cycling?
About 6 m/s.
What is the typical speed of sound in air?
About 330 m/s.
What does a horizontal line on a distance–time graph show?
The object is stationary (not moving).
On a distance–time graph, what does a steeper line mean?
The object is moving faster.
How do you find the speed from a straight line on a distance–time graph?
Work out the gradient of the line: speed = distance ÷ time.
What is the equation that relates acceleration to change in velocity and time taken?
acceleration = change in velocity ÷ time taken, i.e. , in m/s².
What is the value of the acceleration in free fall, g?
10 m/s².
True or false? An object falling at a constant velocity has zero acceleration.
True. Its velocity is not changing, so the acceleration is zero.
What is the equation linking final velocity, initial velocity, acceleration and distance?
, where x is the distance in metres.
What does the gradient of a velocity–time graph represent?
The acceleration of the object.
What does a horizontal line on a velocity–time graph show?
Constant velocity (zero acceleration).
On a velocity–time graph, which part of the line shows the greatest acceleration?
The part with the steepest slope (gradient).
What does a line sloping downwards on a velocity–time graph show?
The velocity is decreasing — the object is decelerating.
What does the area between the line and the time axis on a velocity–time graph represent?
The distance travelled.
True or false? The distance travelled is found from the area under a distance–time graph.
False. Area under a velocity–time graph gives distance; on a distance–time graph the distance is read straight off the axis.
What are the steps to measure the average speed of a toy car in the laboratory using a stopwatch?
e.g. a car rolling along a bench
- Measure the distance between two marks
- Start the timer at the first mark, stop it at the second
- speed = distance ÷ time; repeat and average
How does a single light gate with a card on a trolley measure the trolley's speed?
The card interrupts the light beam; speed = width of the card ÷ time the beam is blocked.
What is the main advantage of using light gates instead of a hand-held stopwatch?
They remove human reaction time (about 0.2 s), which is similar in size to the short times being measured.
How is ticker tape used to find the speed of a trolley?
Measure the distance between dots; the timer makes dots at a known rate (e.g. 50 per second), so speed = distance ÷ time.
Give two ways to improve a measurement of average speed made with posts and a stopwatch.
Increase the distance between the posts, and use an electronic timer or light gates (also: use marks on the track, stand midway between the posts).
What is the difference between distance and displacement?
Distance is how far an object has moved (a scalar). Displacement is the straight-line distance from start to finish, with its direction (a vector).
What is deceleration?
Negative acceleration: the velocity is decreasing. e.g. a deceleration of 3 m/s² is an acceleration of −3 m/s².
On a distance–time graph, what does a curved line show?
The speed is changing: if the gradient is increasing the object is speeding up; if the gradient is decreasing it is slowing down.
How do you find the speed at a particular time from a curved distance–time graph?
Draw a tangent to the curve at that time and work out the gradient of the tangent.
What is a typical wind speed?
About 5–20 m/s.