## Force changes the motion

Consider the process of changing the movement by applying force to the cart.

If the amount of force acting on the cart is doubled or tripled, the speed change is doubled or tripled.

If the force is constant and the mass of the cart is doubled or tripled, the speed change becomes \( \frac{1}{2} \) times and \( \frac{1}{3} \) times .

In other words, when a force is applied to an object, the velocity of the object changes. The degree to which an object's velocity changes is proportional to the magnitude of the force applied and inversely proportional to the mass of the object.

\[ a = \frac{F}{m} \]

'a' is the acceleration. This is the degree to which the speed of motion of an object changes. The unit is m/s².

'F' is the force applied to an object. The unit is N (Newton).

'm' is the mass of the object. The unit is kg.

This is called the 'law of acceleration' or 'Newton's law of motion. This law explains a fairly wide range of natural phenomena. This law can explain from small particles(ex. electrons) to the motion of celestial bodies. (However, This law ignore quantum mechanics and special relativity)