How are you able to shoot a marshmallow closer or further away?
Pulling the spoon down further will make the marshmallow shoot further.
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Grade 4
- Life and Living
- Matter and Materials
- Energy and Change
- Earth and Beyond
- Grade 5
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Grade 6
- Life and Living
- Matter and Materials
- Energy and Change
- Earth and Beyond
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Graad 4
- Lewe en Lewenswyse
- Materie en Stowwe
- Energie en Verandering
- Die Aarde en die Heelal
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Graad 5
- Lewende en lewende
- Materie en Stowwe
- Energie en Verandering
- Die Aarde en die Heelal
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Graad 6
- Lewe en Lewenswyse
- Materie en Stowwe
- Energie en Verandering
- Die Aarde en die Heelal
Energy and movement
- How can stored energy be changed into movement energy?
- How can we make things move using stored energy?
This chapter is an introduction to stored (potential) energy and movement (kinetic energy). Although the proper terms are not used here, you could introduce them in class so that learners start to become familiar with these words for the later grades.
Do you remember in Gr. 4 when we looked at energy and movement in a system? We were mostly looking at musical instruments and how they use movement energy (the input) such as plucking or blowing to make them work.
In this chapter we are going to look some other ways of using stored energy to produce movement energy.
Elastics and springs
Have you ever stretched an elastic band? When you pull it apart and then release it, what happens?
When you release the elastic band, it shoots back into position.
When we stretch an elastic band, we store energy in it. This is because when the band is stretched, it can do work when you release it. We are going to look at some other ways of using stretched elastic bands to do work and produce movement.
Making your own catapult
MATERIALS:
- 10 ice lolly sticks or craft sticks
- 4 to 6 rubber bands
- 1 plastic spoon
- bag of marshmallows
INSTRUCTIONS:
- Place 8 of the sticks together and tie a rubber band tightly around one end.
- Tie another elastic band around the other end so that the sticks are bound tightly.
- Tie a rubber band around the remaining 2 sticks, close to the one end.
- Insert the bundle of 8 sticks bound together through the 2 stick bundle. Look at the image below to see how to do this.
- Tie another rubber band in a cross so that the two bundles are held in place, as shown below.
- Use a rubber band to secure the plastic spoon on the end. You now have a simple catapult.
- Shoot the marshmallows by placing one on the spoon, pulling down, and then releasing it.
- Have a competition to see who can shoot marshmallows the furthest and the most accurate - can you hit a target?!
QUESTIONS:
When the marshmallow goes as far as possible, how much did the elastic band stretch compared to when the marshmallow didn't go far?
The greater the stretch of the elastic band, the further the marshmallow went
Where did the movement energy of the marshmallow come from?
Stored energy in stretched elastic
We saw in this activity that if you stretch an elastic band, you can produce movement. The stored energy in the band - when it is stretched - has the potential to do work. We call the stored energy in the elastic band potential energy because it has the potential to do something for us later. But what does the word potential mean?
Look up a definition for 'potential' in your dictionary.
Having the capacity to do or develop into something in the future. Synonyms are possibility/feasible.
A stretched elastic band can also produce movement and do work in the future when it is released.
Let's look at another way of using an elastic band to produce movement energy. Instead of stretching it, we can twist the elastic band.
Build an elastic band powered boat
MATERIALS:
- rectangular wooden block (about 5 cm by 8 cm by 2 cm)
- 2 ice cream sticks
- 1 piece of plastic (6 cm by 2,5 cm cut from a plastic coffee tin lid)
- 1 large rubber band
- 1 small rubber band
- a tub of water to test your boat in
INSTRUCTIONS:
- Secure the ice cream sticks flat against the sides of the wooden block with a thick rubber band, so that about 1/4 to 1/2 of each stick is extending out beyond the end of the block.
- Place a thinner rubber band across the ends of the sticks.
- Slip the piece of plastic through the thin rubber band.
- Turn the plastic to twist the rubber band.
- Place it in the water, and let it go.
- Challenge: Can you get your boat to move backwards and forwards?
QUESTIONS:
What is the purpose of twisting the elastic band?
The purpose of twisting the elastic band is to store energy in it.
Why does the boat move? Use what you have learnt about potential energy and energy transfer to answer this question.
Stored/potential energy in the elastic band is released in the form of movement energy and transferred to the piece of plastic, which in turn drives the boat.
How could you make the boat move in different directions (backwards and forwards)?
Twist the piece of plastic in different directions. Twisting it towards the boat will make the boat move forwards, twisting it away from the boat will make it move backwards in the water.
Write down what you have learnt about energy from the last two activities that you have completed. Use words like movement energy and potential energy or stored energy.
Elastic bands that are stretched or twisted store energy. The stored energy can be released as movement energy when the elastic band is released and returns to its normal shape.
We have been looking at elastic bands and how they can be stretched or twisted to store energy to do work (to produce a movement). Springs can also be compressed or stretched to store energy.
A slinky is a metal coiled spring. When you stretch a slinky spring it stores energy. When the spring is released, the stored energy is changed into movement energy as it springs back into place.
Springs can also be compressed to do work. To compress something means that you squash it! Look at the photo below of a child jumping on a pogo stick. This pogo stick works using a compressed spring.
Use your knowledge of springs to explain how a pogo stick works. Your answer must include the words compress, stored energy and movement.
When a child jumps on a pogo stick he compresses the spring (squashes it). The spring then has stored energy and releases back up and pushes the child up again. The stored energy from the compression is released and turned into a movement.
- Stored energy can be changed into movement energy.
- Energy can be stored in a stretched or twisted elastic band.
- Energy can be stored in compressed or stretched springs.
A jack-in-the-box is a fun toy. An object jumps out of a box when the lid is opened. Explain how it works.
A compressed spring is under the object. When the lid is opened, the spring is released and the stored energy is changed into movement energy of the object.
Is a stretched elastic band an example of stored or released energy?
stored energy
What else, besides stretching, can you do to an elastic band to give it stored energy?
Twist it.
Think of some examples which you have experienced that use springs to store energy and write them down below.