Did you know that moving objects are kinda like teenagers? They can be stubborn! Objects at rest want to stay at rest, and objects in motion want to stay in motion. This idea was started by Galileo, who thought about how a ball rolling down a ramp would keep rolling if the ramp were flat at the end. This became Newton's First Law of Motion or the law of inertia: "An object remains stationary or moves at a constant velocity unless an external force acts on it."

🚴‍♂️ Real-world example: When you're riding a bike and stop pedaling, you continue to coast along until friction (an external force) slows you down.

Now, let's take a leap back in time to the ancient Greek philosopher, Aristotle. He believed that a constant force was needed to keep an object moving. But over centuries, this theory was questioned, including by scholars during the Islamic Golden Age. By the time of Newton, this idea was debunked. Turns out, an object's velocity (both speed and direction) stays the same unless something from outside applies a force to change it.

🏐 Real-world example: When you toss a ball, it keeps going in the same direction until gravity pulls it down.

Then Newton gave us his Second Law of Motion - "Force equals mass times acceleration." In other words, if you push or pull something, it's going to speed up, slow down, or change direction based on its mass and how much force you apply.

🚗 Real-world example: Imagine driving a car. The heavier the car (mass), the more gas (force) you need to speed up (acceleration).

There are two key points here

• Mass is a scalar quantity (only magnitude, no direction), so the direction of the force and acceleration will be the same.
• Mass is also the force required per unit of acceleration for an object. This helps standardize force units - 1 Newton (N) of force is what's needed to accelerate a 1kg object at 1 meter per second squared (ms^-2).

Lastly, there's Newton's Third Law of Motion - "Every action has an equal and opposite reaction." Essentially, forces always come in pairs. Push on a wall, and it's pushing back with equal force.

🚀 Real-world example: Rocket propulsion. When rocket fuel burns and gas is expelled downward (action), the rocket is pushed upward (reaction).

To test and understand these laws, we need to perform experiments, but they have to be valid. That means the experiment measures what it's supposed to. A good experiment to understand Newton’s second law involves using elastic threads to pull a cart and observing its acceleration.

But be careful! Uncontrolled variables can lead to invalid results. Consider a student who wanted to test Newton's second law by using different weights to pull a trolley. The mass of the entire system changes with each added weight, which was overlooked. A more valid experiment would involve adjusting both the weight on the trolley and the weight being used to pull it.