Machines are used to change force. Machines change the amount of force. When you use a bottle opener you increase the amount of force. You can't open an old-fashioned coke bottle with your bare fingers. But the opener changes the amount of force under the cap and pushes the top off.
Machines change the amount of speed of force.
A conveyor belt is an example of this. Machines can also change the direction of force. A pulley is an example of a machine changing the direction of force. Who can explain how a pulley changes the direction of force. Insert about 2 centimeters of a ruler under the edge of the book.