Year 7 & 8 TOC
Gravity and the Earth
LO: Exploring how gravity affects objects on the surface of Earth
If you throw a ball up in the air, it comes back down. If you jump of a diving board into a pool, you fall straight down. Gravity is a non-contact force that pulls an object towards the centre of the Earth. Without gravity, we’d probably just float away into the atmosphere.
In 1665 Isac Newton was sitting under an apple tree. As he sat, an apple fell to the ground. He looked at the apple and wondered, why did it fall? He couldn’t see anything pushing or pulling it, so why would it fall? He realised that there must be something pulling the apple towards the Earth. This is how he came up with the idea of gravity.
Gravity is the force that attracts an object to the centre of the Earth. No matter where you are on Earth, you’ll be pulled to the centre. Any object with matter has gravity. The more matter something is made of, the strong it’s gravitational field. The Earth has tremendous mass, and so has a strong gravitational field around it, but even you have a weak gravity surrounding you. So what’s mass and weight?
Mass & weight
Mass is a measurement of the amount of matter something contains. Essentially, it’s how many particles or atoms make up the object.
Weight is the measurement of the pull of gravity on an object.
Think of it like this, if you go to the moon, you’ll notice it’s a lot smaller than earth. It has less mass than the Earth. Meaning the Moon doesn’t have as strong a gravitational pull as the Earth.
While you’re on the moon, you decide to jump and quickly realise you can jump way higher! In fact you weigh yourself and realise you weigh less! Weight is a measure of how much gravity pulls on the object.
But, you’re not any smaller or made of less matter than what you were on Earth, even tho you weigh less. This is why mass and weight are different. Now, contrary to what you may have heard, Mass is measured in Kilograms, while Weight is measured in Newtons. So, a brick with a mass of 1 kilogram, will be 1 kilogram anywhere in the universe. On Earth the brick has a weight of 9.8 newton but on the moon it weighs 1.6 newtons.
Changes in gravity
The amount of gravitational force on an object can change due to a number of factors.
The more mass an object has, the greater gravitational pull it will feel.
The further you move away from the Earth, the less gravitational force is on you. If you checked your weight on a plane in the air, you’d probably fined you weigh less.