Cross-curricular extension unit 7

1 PHOTOCOPIABLE © OXFORD UNIVERSITY PRESS

Natural science: Weight, mass and gravity 1 Match the words 1–13 with the pictures a–m.

1 cable 3 lift 5 orbit 7 pull 9 space 11 strong 13 weak

2 heavy 4 light 6 planet 8 push 10 spacecraft 12 support

2 What part of speech is each word in exercise 1? 1 noun cable ________________________________________________________________________________________

2 adjective __________________________________________________________________________________________

3 verb ______________________________________________________________________________________________

3 Here’s an easy way to remember the order of the planets in the solar system. Take the first letter of each word and that’s the first letter of the planet.

My Very Energetic Mother Just Served Us Nachos.

Now label the planets with the words in the box.

Earth Jupiter Mars Mercury Neptune Saturn Uranus Venus

a b

c

d

e

f

g h

i

j

k

l

m

1 ______________

2 ______________

3 ______________

4 ______________

5 ______________

6 ______________

7 ______________

Mercury

2 PHOTOCOPIABLE © OXFORD UNIVERSITY PRESS

4 Read the four sections of text. Which is a force: gravity, weight, weightlessness or mass?

Force A force can be push or pull. When you push open a door, you use a force. When you pull open a door, you use a force.

Gravity and weight Gravity is the pulling force that holds us all down on the Earth’s surface. The force of gravity gives us our weight: it makes us feel heavy.

Everything has a gravitational pull towards everything else; even two people attract each other. The bigger the object, the larger the pull, so the pull of the Earth is much more than the tiny pulls we have on each other. When we sit on a chair, gravity is pulling us down, but the chair is pushing up against us. Take the chair away and the pushing force disappears, and gravity pulls us onto the ground.

Weightlessness When there is no pushing force, gravity makes us fall freely. If we are in a lift and the cable breaks, the lift falls freely, and so do we. With nothing under us, we feel no weight. For a second, we feel weightless. When we are in orbit in space, we are falling towards the Earth but very slowly. We feel no support from our spacecraft because it is also falling towards the Earth. We feel weightless.

Mass Weight = mass x gravity (w = mg). Mass is measured in kilograms (kg). An elephant’s mass (5,000 kg) never changes, but its weight can change because of gravity. When gravity is weaker, objects are lighter. Weight is measured in Newtons (N).

On Earth 1 kg = 9.8 N. So, the elephant weighs 5,000 kg x 9.8 N = 49,000 N.

On the moon a kilo weighs 1.6 N. So, the elephant weighs 5,000 kg x 1.6 N = 8,000 N. The elephant is lighter on the moon.

5 Read the text again and write True or False for sentences 1–8. Correct the false sentences. 1 A force can make things move. ______________________________________________________________________

2 Gravity gets weaker when an object has more mass. ___________________________________________________

3 We feel weight because something is under our feet. ___________________________________________________

4 We are falling when we are in orbit around the Earth. ___________________________________________________

5 We measure mass in Newtons. ______________________________________________________________________

6 If you increase the mass of an object, it will weigh more. _________________________________________________

7 An object’s mass changes depending on the planet. ____________________________________________________

8 An elephant weighs more on Earth than it does on the moon. ____________________________________________

6 Do some research on the internet or in an encyclopaedia. Find out the gravity on the planets below and calculate your weight on each. Where are you the heaviest? Where are you the lightest?

my mass (in kilograms) gravity my weight (in Newtons)

Earth Jupiter Mars Mercury Neptune Saturn Uranus Venus