# Edexcel IGCSE Physics: Double Science 复习笔记：1.2.1 Types of Forces

### Effects of Forces

• Forces can affect bodies in a variety of ways:
• Changes in speed: forces can cause bodies to speed up or slow down
• Changes in direction: forces can cause bodies to change their direction of travel
• Changes in shape: forces can cause bodies to stretchcompress, or deform

The effects of different forces on objects

### Types of Forces

• There are many types of force. Some examples include:
• Gravitational (or weight) - the force between any two objects with mass (like the Earth and the Moon)
• Electrostatic - the force between any two objects with charge (like a proton and an electron)
• Thrust - the force pushing a vehicle (like the push from rocket engines on the shuttle)
• Upthrust - the upward force on any object in a fluid (like a boat on the surface of a river)
• Air resistance (or drag) - the force of friction between objects falling through the air (like a skydiver in freefall)
• Compression - forces that squeeze an object (like squeezing a spring)
• Tension - forces that stretch an object (like two teams in a tug-of-war)
• Reaction force - the force between any two objects in contact (like the upwards force from a table on a book)

Several types of forces acting on different objects

#### Exam Tip

The force of gravity on an object is called its weight. Remember not to refer to this force as simply 'gravity', as this term can mean several different things and examiners will probably mark it as wrong.Similarly, when referring to air resistance, avoid using terms like 'wind resistance' (there is no such thing!) or 'air pressure', which is a different concept. Drag is an acceptable alternative to the force of air resistance.