Contact forces and muscular force

Often, to put a force on something, your body has to touch it, either directly with your hands or feet, or indirectly through a stick or a rope.

Forces that act only when objects are in physical contact are called contact forces.

One of them is muscular force: the force made by your muscles. Walking, running, lifting, pushing, jumping, stretching, kicking a ball, even writing with a pen all use it. It happens when muscles contract and stretch.

Animals, birds, fish and insects use muscular force to move and survive. People have long used animals' muscular force too, for ploughing fields and pulling carts and tongas.

Muscular force works inside you as well. It helps you chew food and push it along your food pipe and gut (you met this in Grade 7). And your heart muscles squeeze and relax over and over to keep your blood moving round your body.