Forces are pushes and pulls that affect how objects move, stop, or change shape. They can explain why something stays still, speeds up, slows down, or keeps a steady pace. Forces are measured in newtons (N) using tools like a newton meter. For instance, if you pull a box with a newton meter, it might take about 6 newtons to get it moving, showing how much force is needed.

There are two main types of forces: contact forces and non-contact forces. Contact forces need objects to touch each other and include friction, drag, upthrust, tension, and thrust. Friction, for example, is what resists motion between two surfaces, while thrust (like from an engine) helps push things forward.

On the other hand, non-contact forces act over a distance. These include gravitational force, which pulls objects towards each other (like Earth’s pull on us), electrostatic force between charged particles, and magnetic force between magnets.

In diagrams, arrows are used to represent forces, with the arrow’s size showing the force’s strength and direction showing which way it acts. For example, a plane has thrust moving it forward, drag pulling it back, weight pulling it down, and lift pushing it up. These diagrams are also helpful for understanding the forces on falling objects, boats, cars, or even people—giving a clear picture of how forces shape motion.

Hooke’s Law – Forces and Shape

In this video, we dive into forces and how they work to squash, stretch, and change the motion of objects. To squash or stretch something that’s just sitting still, like a ball or a spring, you usually need two forces acting from opposite directions. For example, if you want to squash a ball, pushing in from both sides can compress it. If you only push on one side, it will just move in that direction rather than squashing.

When it comes to stretching, springs are a great example. If you pull a spring from each end with two opposite forces, it stretches. Here, the video explains how forces work with tension (the pulling force) and weight (the downward force) to stretch the spring. A key thing to remember is that some materials are elastic—meaning they’ll snap back to their original shape once you stop stretching them. A spring, if it’s elastic, will return to normal after you remove the weights. Other materials, like Blu-tac, are inelastic. If you stretch Blu-tac, it doesn’t spring back; it stays stretched.

The video also introduces Hooke’s Law, which states that for certain elastic materials like springs, if you double the force, the extension (or amount it stretches) also doubles. To test this, you can set up an experiment with weights and measure how much the spring extends with each new load.

For example, if you add 0.1 Newtons (about the weight of a 10g mass), the spring stretches a certain amount. Add another 0.1 Newton, and the extension should double if the spring obeys Hooke’s Law.

But if you stretch it too much, it reaches a point called the elastic limit, where it won’t return to its original shape anymore.

In the end, we see how a graph of force versus extension for a spring following Hooke’s Law is a straight line through zero. But once the spring goes beyond its elastic limit, the line starts to curve.