There are many different kinds of matter, but they all have certain things in common. This chapter reviews the properties of matter, the particles that make up matter and the changes in matter. Forces A force is a push or a pull. There are many forces which affect our lives. Gravity is the force that makes objects pull toward each other.
Friction is the force that causes objects rubbing together to slow down.
When a force causes something to move work has been done. This chapter reviews how forces and energy cause work to be done. Physical Sciences - Machines Simple machines are tools that make work easier. They are the lever, the inclined plane, the wedge, the screw, the wheel and axle, and the pulley. When more than one simple machine is put together, it is called a compound machine.