Force

A force is a push or a pull. When you kick a soccer ball, you are exerting a force on the ball to make it move. A force is described by its strength and its direction. A force’s strength is measured in units called Newtons, named after Sir Isaac Newton. A force is represented by an arrow pointing in the direction of the force, with the length of the arrow indicating the strength of the force.

Forces can act in combination and produce what is referred to as net force. When two forces are exerted in the same direction, you calculate net force by adding the two forces together. If two equal forces are opposed to each other, they tend to cancel each other out. These are called balanced forces. Two unequal opposing forces will produce a net force in the direction of the larger force.

When two surfaces are rubbed against each other, a force called friction is exerted. Friction acts in the opposite direction of an object’s motion. When an object is in motion, friction can slow it down and cause it to stop. The strength of friction depends on the types of surfaces that are in contact, the amount of contact between the surfaces, and the amount of force pushing the surfaces against each other.

There are several types of friction, including static, sliding, rolling and fluid. Static friction occurs when a force is exerted on an object, but the object does not move. When you push a box across a floor, sliding friction occurs in the opposite direction. Rolling friction, seen in wheels and balls, is easier to overcome than sliding friction in similar materials. Fluid friction occurs when an object moves through a fluid, such as when a boat moves through water or when an airplane flies through the air.