### Equations of Motion - SG & Int2

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• #### Message 1.

Posted by BitesizePhysicsTeacher (U15165682) on Tuesday, 4th December 2012

There are quite a few equations for moving objects, so you need to know what all the symbols mean, and what the quantities are measured in.

d - distance - metres - m
v - speed (velocity) - metres per second - m/s
t - time - seconds - s

The equation linking these is -

d = v t or v = d / t or t = d / v

If t is a LONG time, you'll find the AVERAGE speed for the motion.
If t is a SHORT time, you'll be finding an INSTANTANEOUS speed.

When the speed changes we get an acceleration.

a - acceleration - metres per second per second - m/s²
u - initial (starting) speed - metres per second - m/s
v - final (finishing) speed - metres per second - m/s
t - time - seconds - s

The equation linking these is -

a = (v-u) / t or v = u + at or u = v - at or t = (v-u) / a

Sometimes we call the change in speed Δv = (v-u) = at

So that -

a = Δv / t or v = u + Δv or u = v - Δv or t = Δv / a

The average speed, v(bar), during an acceleration can be found by adding the initial and final speeds and dividing by two -

v(bar) = ( u + v ) / 2

The distance travelled during an acceleration can be found in two ways -

1. Area under the speed time graph for the movement - see www.bbc.co.uk/bitesi...

2. d = v(bar) x t

Things at Higher get a bit more complicated......

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