# Charlotte asks the question “How does gravity hold you to the ground?”

Charlotte I can honestly say that I have no idea how gravity holds things down. I have asked my friends and await an answer.

Charlotte, my team seem to agree with me. In the 17th Century Newton and another scientist called Hooke did some great observations and experiments on falling objects and proposed that gravity was an attraction between any two masses AND the attraction was dependant on the size of the masses involved. For example you are attracted by the Earth and the Earth is attracted by you BUT your attraction is so much smaller than that of the Earth it does not affect the motion of the Earth. The attraction between you and the Earth is also dependant upon how far away you are from the Earth. The Moon is attracted by the Earth and the Earth is attracted by the Moon. They are both big bodies so gravity does affect the way they move with respect to each other and this dictates how the Moon orbits the Earth.

Some scientists including Einstein have put forward ideas on how gravity operates but even these are being challenged. There a lots of things which are still unanswered. The question just has to be asked.

Charlotte, the Earth’s circumference can be calculated by multiplying the diameter of the Earth by pi.(π)

# 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?

Mars has two small moons Phobos and Deimos.

A video that may help –

# Maryam (age 10) asked a question on forces. “What do forces have to do with science?”

Maryam

What an excellent question. How do I answer this? Firstly I think we need to know what we mean by science. Here is what my friends said when I asked them the question.

My favourite definition of science is that it is ‘applied curiosity’. People who enjoy science have a curiosity about the physical and natural world that surrounds them. This leads them to investigate it.

Look at the see-saw in the picture above. Why does a small mass seem to balance a larger mass? Lets move the masses around and see if we can get other positions where they balance? This is curiosity in action.

So what about forces, are they part of the natural world or the physical world? What is a force?

The forces we meet every day are pushes and pulls. Pushes and pulls make things move.

Gravity is another force … jump off a chair and you are pulled to the ground, you moved because of the pull of gravity. Another force is friction – how does that affect movement? Force and movement are therefore intertwined. Investigate movement and you are investigating forces. And that leads to lots of questions. Do things always move at the same speed when a force is applied? Curiosity, curiosity, curiosity.

So please show your curiosity by asking more questions and I leave you with a question of your own. Are forces part of the natural world or the physical one, or both, or neither?

I hope this gives you some answers to your excellent question. Any more questions?