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OCR A-Level Physics > 3.1 Motion > Flashcards

3.1 Motion Flashcards

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1
Q

what is the definition of displacement?

A

the distance the object has moved from its starting position (vector quantity of distance)

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2
Q

what is the definition of instantaneous speed?

A

the speed at a specific point in time of a journey

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3
Q

what is the definition of average speed?

A

the total distance / total time taken

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4
Q

what is the gradient on a displacement-time graph?

A

the object’s velocity

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5
Q

what does a straight line (constant gradient) on a displacement-time graph show?

A

a constant velocity

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6
Q

what is the gradient on a displacement-time graph?

A

the object’s velocity

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7
Q

what does a curve indicate on a displacement-time graph show?

A

velocity is not uniform

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8
Q

what does a curve of increasing positive gradient indicate on a displacement-time graph show?

A

object is accelerating (speeding up)

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9
Q

what does a curve indicate on a displacement-time graph show?

A

velocity is not uniform

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10
Q

what is the gradient on a velocity-time graph?

A

the object’s acceleration

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11
Q

what is the area under the curve on a velocity-time graph?

A

the object’s total displacement

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12
Q

what does a straight line (constant +ve gradient) indicate on a velocity-time graph show?

A

constant positive acceleration

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13
Q

what does a straight line (constant -ve gradient) indicate on a velocity-time graph show?

A

constant negative acceleration

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14
Q

what does a flat horizontal line indicate on a velocity-time graph?

A

constant velocity (not changing velocity)

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15
Q

what does a curve indicate on a velocity-time graph?

A

tells us that the velocity change is not uniform (the acceleration isn’t uniform)

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16
Q

what are the five suvat equations?

A 
v = u + at
v^2 = u^2 + 2as
s = ut + 0.5at^2
s = vt - 0.5at^2
s = 0.5(u + v)t
17
Q

when can you use and apply suvat equations?

A

for an object moving with CONSTANT ACCELERATION

18
Q

outline an investigation to see how collisions affect the motion of a trolley

A
  • set up an experiment with a ramp and a trolley at the top with a wall at the bottom of the ramp and a metre ruler in between ramp and wall and a video camera side on to record it
  • measure the length of the trolley, L, turn on the video camera and start recording
  • place trolley on start line and once the trolley has hit the wall stop recording

-to investigate the final velocities of two trolley coliding, position two trolleys on a smooth surface with a metre
ruler parallel
-measure the lengths of the two trolleys, L, and turn on video camera and record, push one trolley so hits other and stop recording

To calculate velocity:
using video analysis software, you can view frame by frame, pick a point of reference on the metre ruler and count how many frames it takes a trolley to pass that point, knowing the frame rate (no. of frames per second), the time, t, taken for the trolley to pass the point = no.of frames for trolley to pass point x 1 second/frame rate
-use L for length of trolley to do v = L/t

19
Q

outline an investigation to see how collisions with a wall and another trolley affect the motion of a trolley

A
  • set up an experiment with a ramp and a trolley at the top with a wall at the bottom of the ramp and a metre ruler in between ramp and wall and a video camera side on to record it
  • measure the length of the trolley, L, turn on the video camera and start recording
  • place trolley on start line and once the trolley has hit the wall stop recording

-to investigate the final velocities of two trolley coliding, position two trolleys on a smooth surface with a metre
ruler parallel
-measure the lengths of the two trolleys, L, and turn on video camera and record, push one trolley so hits other and stop recording

To calculate velocity:
using video analysis software, you can view frame by frame, pick a point of reference on the metre ruler and count how many frames it takes a trolley to pass that point, knowing the frame rate (no. of frames per second), the time, t, taken for the trolley to pass the point = no.of frames for trolley to pass point x 1 second/frame rate
-use L for length of trolley to do v = L/t

20
Q

what is freefall?

A
  • freefall is the acceleration of a body under the action of a gravitational field, with air resistance and buoyancy being ignored
  • objects of different masses fall at the same rate under the influence of gravity
  • freefall occurs when the only force acting on the object is its weight
21
Q

outline an investigation that looks at what affects the motion of a trolley on a slope

A
  • to see how the distance a trolley has rolled effects it’s velocity
  • set up an experiment with a trolley at the top of a ramp with a light gate at the bottom which is also connected to a data logger
  • measure the length of the trolley, the angle of the ramp (theta) and the distance from the chosen start line to light gate, d (mark start line on ramp)
  • place the trolley on the line and let go (meaning u = 0), the data logger will record the time taken for the trolley to pass through the light gate and calculate the velocity at this point
  • change the starting position to vary d
  • repeat to gain average velocities and to reduce error and record results
  • use s = 0.5(u + v)t
22
Q

what is the relationship between acceleration, force and mass?

A

acceleration is directly proportional to the force acting on it but inversely proportional to its mass (f = ma)

23
Q

outline an investigation to determine g using a trapdoor and an electromagnet

A
  • set up a circuit with an electromagnet supporting a steel ball, a switch, a timer and a trapdoor directly underneath the ball bearing
  • when the current is switched off, the ball begins to fall and and the timer simultaneously starts
  • once it hits the trapdoor the timer is stopped
  • the distance, s, between the bottom of the ball bearing and the trapdoor is measured using a ruler and the time, t, is taken from timer readings
  • repeat to get an average for t
  • u = 0 because the ball starts from rest therefore can use suvat —> s = 0.5at^2, rearrange and solve for g
  • alternatively a graph can be plotted of s (y axis) against t^2 (x axis) so the gradient = 0.5g (as y intercept is 0)

(note if the distance is too large air resistance might have a noticeable effect on the speed, also the height can causes uncertainty, ensure accurate measurement)

24
Q

outline an investigation to determine g using lightgates

A
  • use lightgates and a data logger to measure the time e taken fro a piece of card to travel through the light gate as it falls
  • blu-tack can be added to the corners of the card to stabilise it better
  • the data logger can record the velocity or you can use a timer and work out the average velocity of card is given by L/t where L is the length of the card and t is the transit time recorded by the timer for the card to travel through the light gate
  • use a ruler to measure the vertical height of the card above the light gate, s
  • hold the card vertically above the lightgate before releasing it
  • use suvat, u = 0 because initially from rest so use —> v^2 = 2as, rearrange and solve for g
  • varying the height allows a graph to be plotted, v^2 on y axis and s on x axis, gradient = 2g
25
Q

what is braking distance?

A

the distance the vehicle travels after the brakes have been applied until it comes to a stop

26
Q

what is thinking distance?

A

the distance the vehicle travels during the driver’s reaction time (speed x reaction time)

27
Q

what is stopping distance?

A

stopping distance = thinking distance + breaking distance (total distance to stop)

28
Q

what factors can affect thinking distance?

A
  • higher speed
  • tiredness
  • alcohol and drugs
  • distractions (music etc.)
  • age of driver
29
Q

what factors can affect braking distance?

A
  • higher speed
  • poor road conditions (icy or wet)
  • poor condition of tyres
  • poor condition of brakes
  • mass of car (more luggage or people etc.)
30
Q

why is the relationship between speed and thinking distance linear while the relationship between speed and braking distance not linear?

A
  • thinking distance relationship is linear because reaction time is fixed and therefore goes up in multiples
  • braking distance relationship isn’t linear because at higher speeds it takes a longer amount of time to slow down and come to a stop
31
Q

when answering projectile motion questions what must your remember?

A
  • you have to think of horizontal and vertical motion SEPARATELY
  • a projectile has vertical and horizontal components INDEPENDENT of one another
32
Q

why does a projectile follow a curved/parabolic path?

A

projectiles follow a horizontal path because the horizontal velocity remains constant, while the vertical velocity is affected by the perpendicular acceleration due to gravity

33
Q

when answering projectile motion questions with SUVAT what is important to remember?

A
  • the horizontal component of velocity is always CONSTANT and therefore you can use speed = distance/time
  • the vertical component is affected by constant acceleration due to gravity and therefore you must use SUVAT
  • time is common to both of them
34
Q

how do you resolve a velocity vector into its horizontal and vertical components?

A

horizontal component = Vcosθ

vertical component = Vsinθ

OCR A-Level Physics (24 decks)

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