Speed

D. Crowley, 2007

Speed To be able to calculate speed, and to be able

to predict how the forces acting upon an object will affect the speed

Question Some year sevens ran to the end of the field

How fast were they running?

What extra information would you need to answer this question?

What is Speed? What is speed?

What is it measured in?

How can we work out someone’s speed?

You have five minutes to discuss with your partner the above questions…

Speed Speed is a measurement of how quickly something is

travelling at, which can be in m/s; km/h; mph; cm/year etc…

To work out the speed of something, you need to know the distance covered and the time it took to get there

So speed = distance / time

E.g. 30mph = 30 miles traveled in 1 hour

E.g. 10m/s = 10 meters traveled in 1 second

E.g. 1cm/year = 1 centimeter traveled in 1 year

Speed Formula

Speed(s)

Distance(d)

Time(t)

Examples Jack ran 100m in 12 seconds. What speed was he traveling

at?

Jack then ran 100m again, but this time it was much more windy, and it took him 15 seconds. What was his new speed, and why was this different?

My car was going at 50mph for 1 hour. How many miles did I travel

My car was going at 50mph, and I traveled 20 miles. How long did this take me?

Speed

Distance

Time

Examples Jack ran 100m in 12 seconds. What speed was he traveling at?

Speed = 100 / 12 = 8.34m/s

Jack then ran 100m again, but this time it was much more windy, and it took him 15 seconds. What was his new speed, and why was this different?

Speed = 100 / 15 = 6.67m/s (more air resistance)

My car was going at 50mph for 1 hour. How many miles did I travel

Distance = 50 x 1 = 50mph

My car was going at 50mph, and I traveled 20 miles. How long did this take me?

Time = 20 / 50 = 0.4 hours (24 minutes)

Speed

Distance

Time

Forces & Speed How do forces affect speed?

What happens when you travel very quickly (i.e. on a motorway in the car)

What is it so much effort for a rocket to take off into space?

Why is it more fun to be going downhill on your bike, rather than uphill?!

Forces & Speed Forces can affect speed, both positively and

negatively

Forces can help move objects, i.e. a car engine delivers a force to turn the wheels of a car, moving it

For example, cycling downhill is easier than uphill as gravity is helping pull you down

Bike 1 traveling steadily at 10mph - engine is working against slight air resistance

Bike 2 traveling steadily at 100mph - engine is working very hard against large air resistance

Forces & Speed The opposite is true of space rockets, which must

fight gravity to escape the Earth

As you go very quickly you also experience more friction (increased air resistance, which causes you to slow down)

Different surfaces also have more / less friction - think about what is easier to run on, carpet or ice?

Bike 1 traveling steadily at 10mph - engine is working against slight air resistance

Bike 2 traveling steadily at 100mph - engine is working very hard against large air resistance

Experiment How does road surface affect speed?

Next lesson you are going to investigate this…

It is up to you and a partner to plan an investigation to answer this question

The equipment you will be able to use includes: strips of sandpaper; carpet; ramps; string; Newton meter (measure force); marble; ruler; stop-clock