Dr Pusey

Looking at the motion of an object which is moving at a constant speed, we can determine the speed using this equation:

𝑠𝑝𝑒𝑒𝑑 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑡𝑖𝑚𝑒

If Road Runner runs 10 000 metres and it takes him 500 seconds. How fast is he running?

Road Runner is running 20 metres per second!

A Note for Year 10 - General Speed and velocity are not the same thing

But, for almost all applications in the real world, you can consider them to be the same. We will also do this in this class.

If you undertake more Physics beyond this level, you will learn more about the differences

𝑠𝑝𝑒𝑒𝑑 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑡𝑖𝑚𝑒

𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

𝑡𝑖𝑚𝑒

If Wile. E. Coyote runs 500 m East in 100 s, what is his velocity?

Wile. E. Coyote is running with a velocity of 5 metres per second East

SI units (All scientists came together to agree on these):

v – Velocity/Speed, measured in metres per second (m/s)

s – Displacement/Distance, measured in metres (m)

t – Time, normally measured in seconds (s)

If you are given one of these quantities with different units, you must convert them before using them in calculations. If you don’t, the units of your calculation will be different.

Other versions of the equation

𝑠𝑝𝑒𝑒𝑑 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑡𝑖𝑚𝑒𝑣 =

𝑠

𝑡𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =

𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡

𝑡𝑖𝑚𝑒

To get distance: To get time:

To get speed:

𝑠 = 𝑣 × 𝑡 𝑡 =𝑠

𝑣

Example Problems Dr Pusey runs 80 metres in 10 seconds, how fast can he

run?

If the latest fool from Jackass gains a speed of 20m/s on his skateboard, how far will he travel in 5 seconds?

North Korea launches a rocket which reaches a speed of 100m/s towards the international space station which is 50,000m away, how long do the occupants have to escape?

Example Problems Dr Pusey runs 80 metres in 10 seconds, how fast can he

run?

If the latest fool from Jackass gains a speed of 20m/s on his skateboard, how far will he travel in 5 seconds?

North Korea launches a rocket which reaches a speed of 100m/s towards the international space station which is 50,000m away, how long do the occupants have to escape?

𝑣 =𝑠

𝑡

𝑠 = 𝑣 × 𝑡

𝑡 =𝑠

𝑣

Example Problems Dr Pusey runs 80 metres in 10 seconds, how fast can he

run?

If the latest fool from Jackass gains a speed of 20m/s on his skateboard, how far will he travel in 5 seconds?

North Korea launches a rocket which reaches a speed of 100m/s towards the international space station which is 50000m away, how long do the occupants have to escape?

𝑣 =𝑠

𝑡=

80

10=8m/s

𝑠 = 𝑣 × 𝑡 = 20 × 5 = 100m

𝑡 =𝑠

𝑣=50000

100= 500 𝑠 = 8.3𝑚𝑖𝑛𝑢𝑡𝑒𝑠

Converting Sometimes you will need to convert between different

units.

1 minute = 60 seconds How many minutes in 120 seconds?

How many seconds in 3.5 minutes?

1 kilometre = 1000 metres How many metres in 2.14km?

How many kilometres in 3694 metres?

Converting Sometimes you will need to convert between different

units.

1 minute = 60 seconds

How many minutes in 120 seconds? 2 minutes

How many seconds in 3.5 minutes? 210 seconds

1 kilometre = 1000 metres

How many metres in 2.14km? 2140 metres

How many kilometres in 3694 metres? 3.694 kilometres