1. UNIT 3 BAT REVIEW Electromagnetic Force
March 8, 2018

2. Forces A force is a push or a pull
It doesn’t matter if you push or pull
Forces are measured in units called Newtons
You measure force with an instrument called a spring scale

3. Why Are Forces Important?
In order for something to change motion, you need to apply a force.
If you want something to start moving, you need a force
If you want something to stop moving, you need a force in the opposite direction
If you want something to speed up, slow down, or turn, you need a force!

4. Examples of Forces Contact Force – Pushing something
Gravity – Pulls down on you
Magnetic Force – We’ll get to that later
Normal Force – The ground pushing back up on you when you sit or stand.
Friction – See next slide

5. Friction
Friction is the force two objects create when they push against each other.
Friction always acts in a direction opposite of motion. It can keep you from moving or slow you down
You can reduce friction by
Using Wheels (Rolling Friction)
Going on Liquid (Fluid Friction)
Floating on Air (Also Fluid Friction)

6. Adding Forces (Net Force)
If two forces are in the same direction, they add together
If two forces are in opposite directions, they cancel out
If two forces add up to 0N, we say that they are in equilibrium, and motion does not change

7. Newton’s 1st Law of Motion
Newton’s 1st Law of Motion (Inertia) – An object in motion stays in motion in a straight line, and an object at rest stays at rest unless acted upon by an unbalanced force.

8. Newton’s 2nd Law of Motion
Newton’s 2nd Law of Motion – Force equals mass times acceleration
More force means more acceleration
More mass means less acceleration

9. Newton’s 3rd Law of Motion
Newton’s 3rd Law of Motion – For every action, there is an equal and opposite reaction
If I push the door with 200 N of force, the door pushes back on me with 200 N
So we’re in equilibrium and the door doesn’t move

10. Magnetism
A permanent magnet is an object that always exerts a magnetic force
When an object that is ferromagnetic (contains iron, cobalt, or nickel) gets close to a permanent magnet, it becomes a temporary magnet.
So the permanent magnet induces magnetism in the temporary magnet

11. Rules of Magnetism
Every magnet has two poles – a north pole and a south pole
Opposite poles (N/S) attract
Like poles (N/N, S/S) repel
Compasses work because the Earth is a giant magnet

12. Magnetic Fields
A magnet has a magnetic field. Anything ferromagnetic in the field has magnetism induced in it.
Magnetic fields go on forever but get weaker with distance
Magnetic fields can extend through objects like paper.
Magnetic fields are strongest at the poles and weakest in the middle

13. Electricity
Electricity flows in a closed circuit. This is a path that starts at a power source and flows back uninterrupted to the other side of the source.
With batteries, electricity flows from the negative terminal to the positive terminal
Some things that can open circuits are flowing from plus to plus, or an open switch, or flowing to the same part of a component

14. Electromagnets
When electricity flows through a wire, it creates a magnetic field.
If you coil this wire around a ferromagnetic core enough times, the field is strong enough to have a visible effect – we call this an electromagnet
Electromagnets are useful because they can turn on and off

15. Variables That Can Affect Electromagnets
For an electromagnet to work, the coiled wire needs to be insulated
The more coils you wrap around the core, the stronger the magnetic field
The tighter you wrap the coils, the stronger the magnetic field
The thicker the wire, the stronger the magnetic field.
The more voltage (battery power) you have, the stronger the magnetic field

16. Motors A motor converts electrical energy into kinetic energy
It works because it has two wires powering three electromagnets
Since only two electromagnets are on, only those two go to the permanent magnets
But as the shaft moves, one electromagnet turns off and another turns on and it goes to the permanent magnet.
As the shaft keeps turning, this process keeps going

17. Generators
A generator is like a motor, except that it works in reverse
So a generator converts kinetic energy into electrical energy.
Power plants use large generators powered by turbines – the different kinds use different methods to get the turbine to turn.