Forces

1. Gravity

1.1. Weight

2. Wind

2.1. Windmill

2.1.1. Electricity

2.1.2. Ground wheat

2.1.2.1. Flour

3. Mechanical force

3.1. Water mill

3.1.1. Electricity

3.1.2. Ground wheat

3.1.2.1. Flour

4. Pressures of gases

4.1. Gasoline engine

4.1.1. Movement

4.2. Diesel engine

4.2.1. Movement

5. Muscles

5.1. Farmer ploughing

6. Caused by the effects of heat

6.1. Steam engine