UNIT 8

FORCES

PUSHING AND PULLING

-         When we apply force to an object, we push or pull that object.

-         A force always acts in one direction.

USING FORCE

-         We use forces to do many things every day.

-         For example: to open or close a door or a window.

-         We need to apply more force to move heavier objects.

DIFFERENT TYPES OF FORCES

CONTACT FORCES

-         When one object touches another object, the objects are in contact.

-         When one of the objects pushes or pulls the other object, there is a contact force.

GRAVITY

-         Gravity is a force that attracts a smaller object to a larger object.

-         All objects that have mass are affected by gravity.

-         Gravity keeps the Earth and the other planets in the Solar System in their orbits around the Sun.

-         Without gravity, everything would float into space.

MAGNETISM

-         Magnetism is the force that magnets produce.

-         Magnets attract some metals like iron.

-         The ends of a magnet are called poles.

-         Magnetism has two directions. It can pull objects together or away from each other.

MACHINES

MACHINES ARE TOOLS

-         A machine is a tool that makes work easier.

-         There are two types of machines: simple machines and complex machines.

-         Complex machines are two or more simple machines working together.

WORK

-         When we use a force we are doing work.

-         Pushing, pulling and lifting are examples of work.

SIMPLE MACHINES

LEVER

-         A lever is a bar that moves on a point called fulcrum that helps us to move heavy things.

PULLEY

-         A pulley is a wheel with a rope that helps us to lift heavy things.

INCLINED PLANE

-         An inclined plane has an angle that reduce the force needed to move  something up or down.

SCREW

-         A screw is an inclined plane around a shaft that helps us to joint different parts.

WHEEL AND AXLE

-         A wheel spins around and axl and helps us to move objects.

WEDGE

-         A wedge is made of two inclined planes.

-         We use wedges to cut or separate things.

SIMPLE AND COMPLEX MACHINES

-         Complex machines are two or more simple machines working together.

-         A bicycle is an example of a complex machine:

o   Screws are used to joint the parts.

o   The pedals are examples of a wheel and an axle…