3.1 - Motion Flashcards
what is the definition of displacement?
the distance the object has moved from its starting position (vector quantity of distance)
what is the definition of instantaneous speed?
the speed at a specific point in time of a journey
what is the definition of average speed?
the total distance / total time taken
what is the gradient on a displacement-time graph?
the object’s velocity
what does a straight line (constant gradient) on a displacement-time graph show?
a constant velocity
what does a curve indicate on a displacement-time graph show?
velocity is not uniform
what does a curve of increasing positive gradient indicate on a displacement-time graph show?
object is accelerating (speeding up)
what is the gradient on a velocity-time graph?
the object’s acceleration
what is the area under the curve on a velocity-time graph?
the object’s total displacement
what does a straight line (constant +ve gradient) indicate on a velocity-time graph show?
constant positive acceleration
what does a straight line (constant -ve gradient) indicate on a velocity-time graph show?
constant negative acceleration
what does a flat horizontal line indicate on a velocity-time graph?
constant velocity (not changing velocity)
what does a curve indicate on a velocity-time graph?
tells us that the velocity change is not uniform (the acceleration isn’t uniform)
what are the five suvat equations?
v = u + at
v^2 = u^2 + 2as
s = ut + 0.5at^2
s = vt - 0.5at^2
s = 0.5(u + v)t
when can you use and apply suvat equations?
for an object moving with CONSTANT ACCELERATION
outline an investigation to see how collisions affect the motion of a trolley
- 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 colliding, 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
what is free fall?
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
free fall occurs when the only force acting on the object is its weight
outline an investigation that looks at what affects the motion of a trolley on a slope
- 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
what is the relationship between acceleration, force and mass?
acceleration is directly proportional to the force acting on it but inversely proportional to its mass (f = ma)
outline an investigation to determine g using a trapdoor and an electromagnet
- 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)
outline an investigation to determine g using light gates
- use light gates and a data logger to measure the time taken from 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 light gate 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
what is braking distance?
the distance the vehicle travels after the brakes have been applied until it comes to a stop
what is thinking distance?
the distance the vehicle travels during the driver’s reaction time (speed x reaction time)
what is stopping distance?
stopping distance = thinking distance + breaking distance (total distance to stop)
what factors can affect thinking distance?
- higher speed
- tiredness
- alcohol and drugs
- distractions (music etc.)
- age of driver
what factors can affect braking distance?
- higher speed
- poor road conditions (icy or wet)
- poor condition of tyres
- poor condition of brakes
- mass of car (more luggage or people etc.)
why is the relationship between speed and thinking distance linear while the relationship between speed and braking distance not linear?
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
when answering projectile motion questions what must your remember?
you have to think of horizontal and vertical motion SEPARATELY
a projectile has vertical and horizontal components INDEPENDENT of one another
why does a projectile follow a curved/parabolic path?
projectiles follow a horizontal path because the horizontal velocity remains constant, while the vertical velocity is affected by the perpendicular acceleration due to gravity
when answering projectile motion questions with SUVAT what is important to remember?
- 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
how do you resolve a velocity vector into its horizontal and vertical components?
horizontal component = Vcosθ
vertical component = Vsinθ
