BJC FORCE

What is a force?

a push or pull on an object

What is friction?

A force that opposes motion

what 2 factors affect friction?

• the weight acting on each surface

• the nature of the surface

What are 2 ways to reduce friction?

• changing sliding friction to rolling friction

• making surfaces smoother

List 4 ways friction is helpful

• keeps stationary objects fixed

• the operation of brakes in vehicles depends on friction

-the heat from matches depends on friction

• we would not be able to walk without sufficient friction between our shoes and ground

What is gravity?

the force that pulls objects toward earth

What is weight?

the force of gravity on an object

If a person weighs 150N on Earth

what will the person weigh on the Moon?

if a person weighs 24N on the moon

what is their on earth?

What is a magnet?

any material that attracts iron or things made of iron

what are uses for magnets?

• lifts heavy objects

• used in a compass to find direction

• used in telephones

radio and TV's

What is a natural magnet? give an example

a naturally occurring mineral capable of attracting magnetic substances. e.g. lodestone

what is an artificial magnet? give an example

a man-made substance capable of attracting other magnetic substances. e.g. Alnico

What is the law of magnetism?

Like poles repel and unlike poles attract

What is a magnetic field?

The area of magnetic force around a magnet

A magnet is strongest at its…

poles

What is an electromagnet?

A magnet made of an iron core that is temporarily magnetized by an electric current flowing through a coil that surrounds it

What does the strength of an electromagnet depend on?

• the number of turns in wire in the coil

• the amount of current in the coil

How do you demagnetize a magnet?

hammering

What is a machine?

A device that makes work easier

What is a lever?

a bar that is free to pivot

give examples of a 1st class lever

seesaw

give examples of a 2nd class lever

wheelbarrow

give examples of a 3rd class lever

shovel

what is a pulley?

A simple machine that consists of a rope that fits into a groove in a wheel

What is a wheel and axle?

a machine made of a rod and an attached wheel

give examples of a wheel and axle

doorknobs

What is an inclined plane?

a flat

What is a wedge?

A machine made of an inclined plane with one or two sloping sides

What is a screw?

An inclined plane wrapped around a cylinder

what is a complex machine?

A machine is made up of more than one simple machine working together.

give examples of complex machines

hand drill

why does cold air have more air pressure than warm air?

warm air is lighter

why does dry air have more air pressure than moist air?

moist air is lighter

single pulley system

A pulley system that uses one wheel

double pulley system

A pulley system that has two wheels that are connected.

movable pulley

a type of pulley that moves with the load

fixed pulley

A pulley attached in position above a load to be lifted.