Jessica (8) asks – How do the planets orbit the Sun? How many moons does Mars have?

Jessica. A great question. You also asked a question about the Moons of Mars so I will try to answer them both here. Firstly I asked my friends about the orbits of the planets.

Sometimes I think they tackle the easy bits and give me the hard bits.

Lets look at what we mean by a force. A force is a push or pull on something that you are interacting with. You are applying a force on somebody when you push them away or you are applying a force on something when you pull them to you. When you let go of them the force ends. When you are throwing a ball you are only applying a force in the throwing process. When you let go of the ball the force that you were applying ends.

Simple, but

Some of the forces can be applied without touching the thing you are forcing. Magnetism is an example one magnet will apply a force to another magnet without touching and  Newton realised that when objects fall towards the ground they fall because the Earth is applying a force on those objects. He called that force Gravity.

Now what is happening to the planets. Here is a little experiment. Tie a ball to a piece of string (a polystyrene ball would be the best). Now holding the end of the string spin the ball around your head (probably best to do this in the garden). Can you feel the tug(force) being applied on your hand. Now let it go. What happens? Does it just drop to the ground. Now think about this. The ball is a planet and your hand is the Sun. Not only gravity but another force linked to the speed of the flying ball and it’s mass is in action. Maybe it is the application of these two forces that make planets orbit the Sun?