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Kinematics -
describing motion
- speed
- you can calculate the avrage speed of
something moving if you know the distance it
moves and the time it takes. For this you use
the equation, average speed = distance / time.
In symbols this is written as V = X / t
- If the object is moving at a constant speed
this equation will give us the speed during
the time taken. If the speed is changing
then the equation gives us average speed.
- If you look at the speedometer in
a car, it doesnt tell you the
average speed. It tells you the
insantaneous speed, this is the
speed at the instant you look at it.
- you can calculate the avrage speed of
something moving if you know the distance it
moves and the time it takes. For this you use
the equation, average speed = distance / time.
In symbols this is written as V = X / t
- units
- Systéme Internationale d'Unités (SI system),
distance is measured in metres (m) and time
in seconds (s). Therefore, speed is in metres
per second ms-1 (or as m/s)
- Systéme Internationale d'Unités (SI system),
distance is measured in metres (m) and time
in seconds (s). Therefore, speed is in metres
per second ms-1 (or as m/s)
- laboratory measurments of speed
- two light gates
- use a trolley with a section of card attached
to it and accelerate it forward, the edge of the
card breaks the first light beam which starts
the timer. when the second beam is broken
the thimer stops. from this the computer
works out the speed from the time interval
and the distance between the two gates
- use a trolley with a section of card attached
to it and accelerate it forward, the edge of the
card breaks the first light beam which starts
the timer. when the second beam is broken
the thimer stops. from this the computer
works out the speed from the time interval
and the distance between the two gates
- one light gate
- similar to using two light gates but
insead of the dictance between two
light gates, the length of the csrd is
used. The computer uses the time
taken from the beam being broken
to the beam rejoining and the length
of the card to work out the speed
- similar to using two light gates but
insead of the dictance between two
light gates, the length of the csrd is
used. The computer uses the time
taken from the beam being broken
to the beam rejoining and the length
of the card to work out the speed
- ticker timer
- a ticker timer marks dots on a tape at regular intervals. Attach
the tape to the trolley and push it. The spacing of the dots will
indercate the movement: even spaces show constant speed
and increasing spaces show increasing speed. Measure the
distance of every fith dot from the start, this will give you the
trolleys distance at intervals of 0.1 seconds
- a ticker timer marks dots on a tape at regular intervals. Attach
the tape to the trolley and push it. The spacing of the dots will
indercate the movement: even spaces show constant speed
and increasing spaces show increasing speed. Measure the
distance of every fith dot from the start, this will give you the
trolleys distance at intervals of 0.1 seconds
- motion sensor
- A motion sensor transmits regular
pulses of ultrasound at a moving
trolley, the computor then records the
time it took for the waves to reach the
tralley and get back. From this the
computor can work out the speed at
which the trolley was travelling
- A motion sensor transmits regular
pulses of ultrasound at a moving
trolley, the computor then records the
time it took for the waves to reach the
tralley and get back. From this the
computor can work out the speed at
which the trolley was travelling
- which is the best method?
- Does the method give
and average speed or can
it be used to give the
speed at different points?
- how percisely does the
method measure time?
- how simple and convenient is
the method to set up in the lab?
- Does the method give
and average speed or can
it be used to give the
speed at different points?
- two light gates
- distance and displacement,
scalar and vector
- distance
- how far that was
actually travelled
- how far that was
actually travelled
- displacement
- distance moved in a
particular direction
- distance moved in a
particular direction
- scalar
- has just magnitude e.g. distance
- has just magnitude e.g. distance
- vector
- has both magnitude and
direction e.g. displacement
- has both magnitude and
direction e.g. displacement
- distance
- speed and velocity
- Its important to know the speed of an
object and its direction, these two
quantities can be combined to form
another quantity called velocity
- Velocity can be thought of as
speed in a particular direction,
this makes it a vector quantity.
- since velocity is a vector quantity it is defined
in terms of displacement so the equation is:
velocity = change in displacement / time taken
- the definition of velocity is: the rate
of change of an objets displacement
- Its important to know the speed of an
object and its direction, these two
quantities can be combined to form
another quantity called velocity
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