Like last week, this week’s project is all about forces. As usual, just do your best, but don’t worry if you don’t complete all the work…
GOAL: Gravity and Friction
As you’ve already learned, forces make objects move. As well as Pushes and Pulls there are also forces called gravity and friction.
Pick up a pencil. Now, let go of it. What happens? Of course, it falls. The force that causes something fall is called gravity. Gravity is caused by the pull from really huge objects.
What does gravity do for us?
- The Sun is enormous so it has a huge gravity force – it keeps the Earth circling it
- The Earth is very big so gravity is a fairly strong force here.
- The Moon is 1/6 the size of the Earth, so its gravity force is 1/6 as big (that’s why astronauts can bounce high on the Moon)
Task 1 – Watch a Gravity Clip
Watch this BBC BiteSize video to introduce gravity:
Task 2 – Watch a Friction Clip
Now, put something (an apple?) on the floor and push it. What happens? Of course, it rolls for a while and then stops. But why does it stop?
If you did this in space, the apple would not stop! It would just keep going. Something on Earth causes things to stop moving. This “stopping force” is called friction. Friction happens when two things move against each other. Try skidding across the floor – your shoes have grips which create lots of friction so it’s hard to slide. Socks, however, have little friction so it’s far easier to slide.
Now watch this clip from BBC BiteSize on friction:
Task 3 – An Investigation
I tried to think of the most fun investigation you could to do with forces. I hope you like this one! You’ll need to make a paper helicopter and then test it when it falls. The blades (wings) on the helicopter touch the air. The meeting of the air and the blades causes friction. This type of friction is called air resistance. Air resistance slows things down.
Here is a template of the helicopter you can use:
Now, cut along the solid lines and fold on the dotted ones. Here is a website to show you a little more:
You can colour it with felt tips if you like. Throw it into the air and see what happens – it should spin. Add a paper clip to the bottom of it. Does it spin better? It usually does because it just makes it a little heavier and steadier.
In your experiment, you are going to time how long it takes for the helicopter to fall to the ground. You are going to repeat this but each time the blades will be 1 cm shorter. If the blades are shorter, there should be less paper touching the air – so less air resistance. If there is less air resistance, the helicopter should move more quickly.
How to start:
1. Make the helicopter
2. Write this title on a new page in your book:
GOAL: To Investigate Whether Shorter Blades Create More or Less Air Resistance
3. In your book, write:
I think that a shorter blade will create more / less air resistance. (you decide whether to write more or less)
4. Measure the length of your blade (say it is 10cm)
5. Hold the helicopter out and then drop it. Count how long it takes to hit the floor or look at the seconds on a clock. If you have someone helping you, one of you could use a timer on a watch.
6. Once you have dropped the helicopter x3 times, cut 1cm off both blades. Time its drop x3 times again. Repeat until there are no blades left!
7. In your book, write Results and either stick or draw a results table:
8. Finally, in your book, write:
The shorter the blades of the helicopter, the slower / quicker it falls to the ground. This is because air resistance is less / more if wings are shorter.
If you’d like a little more to do, you could make a new helicopter and try the whole investigation again. However, keep the blades the same length and just add an extra paper clip each time. This will investigate what difference the weight will make (actually, in science the weight is called mass!) to the pull of gravity.
I hope you enjoy this investigation and please send pictures of your investigation to our gallery; I’d love to see them.