# 16.19 Why do things stop moving if we don’t push or pull them?

16.19 Why do things stop moving if we don’t push or pull them? I suggest that you read posts 16.2, 16.4, 16.12 and 16.13 before this. According to Newton’s second law (post 16.2), an object will keep on moving for ever unless we do something to stop it. To make a moving object slow down… Continue reading 16.19 Why do things stop moving if we don’t push or pull them?

# 16.18 What is life?

If you are reading this, you must be alive; the device you are reading it on (computer, tablet, phone) is not alive. The science of living things is a specialised subject called biology. You might then expect that we can define what makes something alive. Usually living things are defined to have several characteristics which… Continue reading 16.18 What is life?

# 16.17 Weight

Before you read this, I suggest that you read posts 16.13 and 16.16. In science the weight of an object is the force exerted on it by a gravitational field (post 16.16). We measure mass in kilogrammes (post 16.13) and weight in newtons (post 16.13) because it is a force. In everyday English we say… Continue reading 16.17 Weight

# 16.16 Gravity

Before you read this, I suggest you read posts 16.12 and 16.13. When we push or pull something we change its motion by exerting a force on it (post 16.13). Now suppose I’m holding an object. The object is not moving (in my frame of reference). But if I stop holding the object, it drops.… Continue reading 16.16 Gravity