Types of Force
Force is a push or pull.
4 Fundamental Forces
There are only four fundamental forces in the Universe.
|These two happen at the atomic level:|
|And these two we experience every day:|
Let's learn more about the last two.
Contact forces, friction and air resistance are all due to this force!
Electrons on one surface repel electrons on the other surface. This leads to contact force:
Friction is the force that pushes back when things try to slide past each other
Two rough surfaces trying to slide past each other.
Without friction we couldn't go anywhere!
A bit more friction, please!
But friction also causes wear and tear on mechanical equipment, so it is not always helpful.
Air resistance (also called drag) is a type of friction. It is greater at higher speeds.
Electromagnetic force also includes magnetism, which acts at a distance: like charges repel each other and unlike charges attract.
Gravity is the attraction of objects with mass or energy towards each other.
It can, for example, make an apple fall to the ground:
Imagine you hold an apple against gravity: the force from the apple is called weight.
Talking About Force
We use special words when talking about force:
Reaction Force: the force that pushes back when another force is applied.
Pushing on this stone gets a reaction force in return.
An Action Force gets a Reaction Force.
The weight of a car gets a reaction force from the road.
Force can be a push or pull:
An object can be in tension or compression:
Tension or compression can be important! For example concrete is very strong in compression but breaks easily in tension, so they often put steel inside concrete to give it strength in tension.
A turning force (which is force times distance) is called a torque (or moment):
Moment or Torque
An object twisted by forces is in torsion: