P2.1 - Motion Flashcards
Disadvantage of using a ruler to measure distance
It is difficult to measure very small or very large distances
Disadvantage of using a stopwatch to measure time
There is a reaction time involved with starting/stopping the timer which affects the accuracy and precision
What can be used to measure very short periods of time?
Light gate which automatically stops a timer when an object interrupts a light beam
What can be used to measure distance?
Ultrasound - measures the time taken for a pulse to travel there and back. It calculates distance using this time and speed of the pulse.
Uniform motion
Speed does not change
Non-uniform motion
Where speed does change
Equation s = d/t gives you the average time, how/why?
Because usually your speed is non-uniform. You cannot be moving at 10 m/s constantly hence it is average
SI Unit for distance
Metres, m
SI Unit for time
seconds, s
SI Unit for speed/velocity
metres per ssecond, m/s
How to convert from 1cm3 to m3
(1x1x1) = (100x100x100)
How many metres in a mile?
1609 metres
How many seconds in an hour?
3600 seconds (60x60)
Vector
Gives magnitude and direction - these are represented by arrows, with a given size
Scalar
Shows only magnitude
Distance
Length of the path that is actually taken (this is a scalar)
Displacement
The shortest distance between two points (this is a vector)
Why are vectors more useful?
They provide more accurate information about what a body is doing
What is the difference between speed and velocity?
Speed is a scalar quantity (it only gives magnitude), whereas velocity is a vector quantity (it gives both magnitude and direction)
How to add vector quantities?
- if they go opposite directions, CANCEL OUT
- if they go same direction, ADD
Acceleration
Rate of change of velocity
SI unit for acceleration
m/s^2
Is acceleration a vector?
Yes. - negative acceleration is known as deceleration
Equation for acceleration
a = v-u/t (final v -initial v over time)
What is acceleration due to gravity
10m/s^2
If there is a change in direction, is that a change in acceleration
Yes since it is a vector
What does a distance time graph show?
Shows how the distance of an object changes with time (Time on x axis and distance on y)
What is the gradient of a distance time graph?
Speed/velocity (due to the equation)
Steep gradient on distance time graph
The body is moving fast.
On a distance time graph, the slope can never go down
True
Straight line on d.t graph
Constant speed, no acceleration
Horizontal line on d,t graph
Body not movin, stationary
Displacement time graph
The same as distance time, but considers direction.
THE GRADIENT CAN BE NEGATIVE FOR THIS
Gradient on displacement time graph
Give velocity NOT SPEED
Velocity time graph shows…
How the velocity of a body changes over time
Gradient on a velocity time graph
Acceleration
Horizontal line on v.t graph
Constant speed, 0 acceleration
Straight diagonal line on v.t graph
Constant acceleration (the steeper the line, the faster the body is accelerating)
Line going up then sloping flat (gradient becomes shallow) on a velocity time graph
Decreasing acceleration
Line going up and becoming steeper on v.t graph
Increasing acceleration
Area under a velocity time graph
Displacement
Equation of motion
v^2 -u^2 = 2as
Kinetic energy equation
KE = 1/2 (m)(v)^2
Area under a speed time graph
Distance
Kinetic energy
The energy of a body owning to its velocity
What happens to KE if the mass doubles/halves?
If mass doubles:
KE doubles
If mass halves:
KE halves
What happens to KE if velocity doubles /halves:
If it doubles:
(2v)^2 = 4
KE will multiply by 4
If it halves:
(v/2)^2= v/4
KE will divide by 4
