What forces are

A force is a push or pull that acts on an object. Forces can change how objects move or behave, and they are measured in units called newtons (N). This measurement helps us understand how strong a force is.

Forces come in different types, depending on whether they need objects to touch or not. We can group them into contact forces and non-contact forces.

Types of forces

Contact forces:

• These require physical touch between objects to act.
• An example is friction, which happens when two surfaces rub against each other and can slow down motion.

Non-contact forces:

• These can act at a distance without objects touching.
• Gravitational force, which pulls objects toward each other, like Earth pulling things down.
• Magnetic force, which attracts or repels objects with magnetic properties.
• Electrostatic force, which acts between charged objects, like when static electricity makes hair stand up.

Effects of forces

Forces can cause various changes to objects. There are five main effects that forces have, depending on the situation. These effects help explain why things move or change in the world around us.

The five effects of forces

• Starting or speeding up motion - A force can make a still object begin moving or make a moving object go faster. For example, kicking a ball starts its motion.
• Slowing down or stopping motion - A force can reduce the speed of a moving object or bring it to a complete stop. Friction from brakes on a bike does this.
• Changing direction - A force can alter the path of a moving object. For instance, hitting a tennis ball with a racket changes where it goes.
• Rotating objects - A force can cause an object to spin or turn around a point. Turning a doorknob applies a force that rotates the handle.
• Changing shape - A force can deform an object, making it bend, stretch, or squash. Squeezing a sponge changes its shape.

Force diagrams

Force diagrams are drawings that show the forces acting on an object. They use arrows to represent each force. The direction of the arrow shows which way the force is pushing or pulling, and the length of the arrow shows the magnitude, or strength, of the force (longer arrows mean stronger forces).

These diagrams help us calculate the resultant force, which is the overall effect of all the forces combined. To find the resultant force, add up the forces in the same direction and subtract those in opposite directions.

How to use force diagrams

1. Draw the object as a simple shape, like a box.
2. Add arrows from the object, pointing in the direction of each force.
3. Label each arrow with the type of force and its size in newtons.
4. Calculate the resultant force by combining the different forces.
   • For example, let's say two forces push right (5 N and 3 N) and one pushes in the opposite direction to the left (4 N)
   • Resultant force = (5 + 3) - 4 = 4 N to the right

Balanced and unbalanced forces

When multiple forces act on an object, they can be balanced or unbalanced. This determines whether the object's motion changes.

Balanced forces

Balanced forces are equal in size but opposite in direction. They cancel each other out, so there is no overall change in the object's motion. The resultant force is zero.

For example, if you push a book with 10 N to the right and someone pushes back with 10 N to the left, the book stays still because the forces are balanced.

Unbalanced forces

Unbalanced forces are not equal, so they do not cancel out completely. This creates a resultant force that is not zero, causing the object to accelerate (speed up or change direction) or decelerate (slow down).

For example, if a car is pushed with 20 N forward and friction pushes back with 10 N, the resultant is 10 N forward, making the car accelerate.