The force that pulls things to the ground on Earth (and other planets) is called gravity.
Gravity also holds Earth and the other planets in their orbits around the Sun.
Gravity is a very useful force – It keeps us on the Earth, and keeps the Earth and the other planets revolving around the Sun. It holds everything together, which is why it has been called ‘The Universal Glue’.
Although the force of gravity also exists on the Moon it is not as strong as it is here on Earth. This is because the Moon is much smaller than the Earth it is not as heavy as the Earth, and so gravity is much weaker there.
In the past people thought that heavier things fell faster than light things. Galileo, an Italian scientist from the 1600’s, conducted some experiments and found that things with different weight fell at approximately the same speed.
Friction is a force between two surfaces when they are moving or sliding across each other. For example, when you try to push your hand across a table. Friction will make this difficult.
Friction works in the opposite direction to which the object is moving. Friction always slows a moving object down, and may even stop an object from moving.
The amount of friction depends the two surfaces.. The rougher the surface, the more friction, the smoother the surface, less friction.
Friction also produces heat. If you rub your hands together quickly, can you feel them get warmer?
The ways friction can help include:
preventing our shoes from slipping on the footpath when we walk
stopping car tyres from skidding on the road
allowing bicycle brakes to grip and slow or stop a turning wheel
Sometimes we want to reduce friction. For example, we use oil to reduce the friction between the moving parts inside a car engine. The oil holds the surfaces apart and can flow between them. The reduced friction means there is less wear on the car’s moving parts and less heat produced.
Ice causes very little friction, which is why it is easy to slip over on an icy day.
However, this is a good thing for ice skating and sledging.
What makes our bikes go? what makes them stop when we brake? Why do apples fall from trees?
After our experiments today watch this video and read through the following information.
You have probably heard the word “force” before. Here are a few examples: “the rocket had a lot of force at blast off” or “the force of the storm blew the roof off the building.” What is force? Force is defined as a push or pull on an object.
When your foot pushes against the pedal of your bike the push makes the wheels of the bike move. When an apple falls from a tree, it is pulled to the ground by gravity.
Forces affect how objects move. They may cause motion; they may also slow, stop, or change the direction of motion of an object that is already moving.
Force can change a number of things about an object. They include:
both direction and speed
Some examples of force changing the direction of an object.
A good soccer player can control the motion of a soccer ball by applying a force that changes the ball’s direction but not its speed.
Swinging a ball on a string around your head.
Some examples of force changing the direction and speed of an object.
A tennis player returning a very fast serve.
Starting on a swing.
Some examples of force changing the shape of an object.