Centre of Gravity Part 1 The centre of gravity is the point where something is most balanced. Our centre of gravity is around our middle. Let’s test it!
Stand side on against a flat surface, like a wall or door. Your shoulder and foot should be against the surface.
Try and lift your outer foot out to the side, without your shoulder or foot leaving the flat surface. You can’t hold on to anything.
You should find it impossible! Try it again but this time don’t stand against the wall. Notice how your body tilts slightly in the opposite direction?
This is because your body needs to balance, otherwise you would fall over! You can’t do it when stood against the flat surface because it is blocking your body from tilting to balance!
Centre of Gravity Part 2
We can’t move our centre of gravity, so we’re going to make something instead!
Try balancing your lollipop stick on your finger, stood on one end. It falls over! You need to move it’s centre of gravity.
Take a pipe cleaner and wrap it round the bottom so that it is hanging down like a leg, do the same with the other pipecleaner.
It should look like your stick has 2 legs!
Clip a binder clip to each leg.
Try balancing it now, it should stand up!
If it falls over, make sure the legs are straight down below the stick.
If you move the legs slightly you should be able to get it to balance in different postitions!
Energy can’t be made or destroyed, only transferred! Here is Chemical Cress to give us some examples of this – [embedyt] https://www.youtube.com/watch?v=5ehqvjiJWmI[/embedyt]
Take your jumping popper and turn it inside out
Squeeze the sides together and then quickly place it on a surface and step back.
It should pop into the air!
Which types of energy can you spot when using your jumping popper?
Struggling to use your jumping popper? Watch the video below for more help!
You are turning your chemical energy from your food into kinetic energy to turn the popper inside out, which becomes potential energy, which becomes kinetic energy, sound energy and heat energy when it pops!
Newton’s 3rd Law
Issac Newton is a famous scientist who lived in in the 1700’s. He helped us to understand a lot about physics, especially forces! Newton’s 3rd law states that each action has an equal and opposite reaction. For example, if you you a push up, you push down against the floor but your body moves in the opposite direction. Another way you can show this is by using a balloon! Note: Take care when using balloons. Children should be supervised at all times and balloons should be kept away from children under 3 and pets.
Inflate your balloon – you may want to use a pump or ask a grown-up to do this for you. Don’t tie the end.
Let your balloon go!
Notice how the air rushes out of the balloon in the opposite direction to the way it flies? It is an equal and opposite reaction.
This time, blow up your balloon, don’t tie it, and tape the tube section to the middle of the balloon.
Thread the string through the balloon, you will need someone to hold the other end or you could attach it to a surface.
You will need to hold the string tight, so the balloon is at one end, with the neck of the balloon at the end of the string and the tube on top of the balloon.
Let the balloon go, it should travel along the string to the other end!
Newton said that things could only be moved from one state (solid, liquid or gas) to another by heating and cooling. He was wrong! Scientists have since found things that can turn from a liquid to a solid in other ways. You are going to try one now.
You may want to do this experiment outside, or with a table cover!
Pour your cornflour into a bowl
Gradually add water to cornflour, a few drops at a time, until it is just a liquid.
You should find that the mixture can change from a solid to a liquid with just a change in pressure. If you hit the liquid it will be hard and solid but if you touch it slowly, your fingers will sink into it like a liquid!