Everything Science Grade 10

CHAPTER 21. MOTION IN ONE DIMENSION 21.5

of the motion.

b. Calculate the acceleration of the aeroplane during the next 20 sec-

onds of its motion.

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(1.) 009q (2.) 009r (3.) 009s

Instantaneous velocity

and speed

ESAGZ

Sprinters taking off

Sprinters finishing race

Photographs by wwarby on Flickr.com

We have looked at the average velocity and

speed but sometimes we want to be more

precise about what is happening between the

initial and final times in a problem.

Instantaneous velocity is the velocity at a spe-

cific instant in time. This can be different to

the average velocity if the velocity isn’t con-

stant.

Look at the photographs of the sprinters in a

race. Their velocity is different as they take

off and as they end. Their average velocity

for the race doesn’t change but their instanta-

neous velocity, as captured in the “snapshots”

of an instant in time does change. Their ve-

locity in the photograph would be an instan-

taneous velocity.

Tip

An instant in time

is different from the

time taken or the time

interval. It is there-

fore useful to use the

symboltfor an instant

in time (for example

during the 4thsecond)

and the symbol∆tfor

the time taken (for ex-

ample during the first

5 seconds of the mo-

tion).

DEFINITION: Instantaneous velocity

Instantaneous velocity is the change in position over the change in a very

small time interval (∆t≈ 0 ).

Quantity: Instantaneous velocity (~v) Unit name: metre per second

Unit name: m·s−^1

Physics: Mechanics 405