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Rogue Physicist.  Free resources for physics education 2006-2016 Dorian Pascoe.  Email: dorian@top-school.co.uk

Most resources are available under a Creative Commons Licence.  Visit our mirror at www.physicsweb.altervista.org

 

 

Energy & Power I

Objectives

Know that power is measured in units of Watts

Be able to calculate the power of a human, based on information about the work done and the time taken.

 

 

Task 1 - Recap

Remind the person next to you:

The units used to measure efficiency

What is meant by "an efficient device"

What is meant by "an inefficient device"

 

 

Task 2

Discuss what you think the word power means.

Where have you heard the term power used?

Power is measured in units called "Watts" - try think of anywhere you might have seen a power rating written on an appliance before.

 

 

 

Task 3

We are going to measure our own power outputs - how powerful we are. We will do this by doing some work (using energy), and timing how long it takes.

 

We will do some work in one of the following ways:

 

1. running up a flight of stairs

or

2. climbing up and down onto a stool 10 times.

 

Your teacher will tell you which method to use. Complete your results in the first row of the table you have been given.

 

n.b. ready made results tables are available for both the stair-climbing practical task, and for the stool-jump practical task.

 

 

Task 4

Collect the weights and times for 9 other people and fill these in on your table, then complete the table by calculating the work each person has done and how powerful they are.

 

You will need to use the following formulae:

 

 

W = F d

 

W = Work done, measured in Joules (J)

F = force, measured in Newtons (N)

d = distance, measured in metres (m)

 

and

 

 

P = E t

 

P = Power, measured in Watts (W)

E = Energy transferred, measured in Joules (J)

t = time taken, measured in seconds (s)

 

 

 

Task 5 - Extension

Answer the questions below:

1. Who are the three most powerful people in the room in order?

2. How many 40W lightbulbs could you power?

3. How many 11W "energy efficient" lightbulbs could you power?

4. A horse can produce a peak power of 750W. How many students would need to work together to be as powerful as a horse?

5. A particular car has a power rating of 150horsepower. How many Watts is this?

 

Watts and horsepower are not the only units we could use to measure power - look at this graph showing the power output of different animals!

 

 

 

Homework

Find the power rating of at least 8 appliances from around your home and estimate the amount of time each one is switched on during a typical day.

 

[Teacher note: make a ready made results table for this task and link it in here.]