## Newton’s First Law

Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.

**TLDR**: A non-zero net force will induce a change in velocity (an acceleration).

### Examples

**Car Crash**: A person not wearing a seatbelt during a crash will continue their motion forwards as the car suddenly stops.**Ball**: A ball rolling on a soccer field will come to a stop because of the friction force acting upon it, creating a negative acceleration (deacceleration).

## Newton’s Second Law

Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration. $F=m \times a$

**TLDR**: The acceleration created by a force depends directly upon the mass of the object.

### Examples

- A student pushing a trolley can cause a great deal of acceleration
- A student pushing a car will cause very little (or no acceleration)

## Newton’s Third Law

For every action, there is an equal and opposite reaction.

**TLDR**: Objects exert an opposite and equal force as a kind of *support*.

### Examples

**Rockets**: Gas is ignited causing it to heat and expand. It is expelled out a narrow nozzel at a high velocity. An equal and opposite force is exerted on the spacecraft causing it to move forwards.**Bouncing Balls**: A ball thrown on the ground exerts a force on contact, the ground exerts an equal and opposite force which causes the ball to bounce.

## Pātai

With the person next to you, write a paragraph describing how Newton’s 1st and 2nd Laws relate to projectile motion.

### Whakatika

- Newton’s 1st Law
**A non-zero net force will induce a change in velocity (an acceleration)**- In the x-direction there are no forces acting (friction is negligible), and in the y-direction there is only the weight force of the object. This means the resultant force is in the downwards direction.
- An acceleration is therefore induced in the downwards direction (constant).

- Newton’s 2nd Law
**The acceleration created by a force depends directly upon the mass of the object.**- In Earth’s gravitational field at sea level, $g=9.81ms^{-2}$ at all times, and therefore the object is accelerated uniformly down.

## Whakawai/Practise

- Try Q1-3 of Activity 10A: Using Newton’s Laws in your textbook.
- Draw a diagram each time!