# Newton's Laws

Sir Isaac Newton proposed three universal physical laws for the concept of motion which are now known as 'Newton's Laws of Motion'. These laws allow us to understand the concept of motion and apply them to everyday life.

### Newton's First Law:

Newton's First Law states that:

*An object maintains its state of rest of constant velocity unless it is acted on by an external unbalanced force.*

### Newton's Second Law:

Newton's First Law of Motion allows us to understand scenarios where the forces are balanced, meaning no acceleration occurs. However, Newton's Second Law of Motion gives us an understanding of scenarios where the forces are unbalanced, meaning that acceleration does occur.

Newton's Second Law of Motion states that:

*The acceleration of an object varies in direct proportion to the external unbalanced force applied to it and inversely proportional to its mass.*

From Newton's Second Law we are given the formula for finding force:

**F = ma**

Where **F** is the force applied on the object [the unit of force is the newton (N)], the mass of the object is **m**, and **a** is the acceleration of the object.

We can also rearrange this formula to find the mass of the object (m = F/a) and the acceleration (a = F/m).

An example of Newton's Second Law of Motion in real life is if you were standing at the top of a cliff and throw a rock over the edge. As the rock hurtles towards the ground it accelerates due to gravity. This is because there is no upward force to balance the downward force of gravity.

### Newton's Third Law:

Newton's Third Law of Motion shows us that forces come in pairs.

Newton's Third Law states that:

*To every action there is an equal and opposite reaction.*

In other words, if an object A exerts a force on another object B, then the object B exerts an equal and opposite force on object A. An example of Newton's Third Law of Motion in action is when you lean against a wall. You are exerting a force on the wall as you lean on it and the wall is also exerting a force on your body to hold it up. In other words, the wall pushes you back as it holds your body up. In some situations it can be difficult to determine the action and reaction pairs in the situation. Here are some examples of action and reaction pairs:

### Concept Questions:

Here are some simple concept questions to help you understand Newton's Laws of Motion. You may work through these individually or as a group, but remember to ask your teacher for help if you get stuck.

1. Explain how Newton's first law applies to these scenarios:

(a) When you hands are wet you flick them and the water flies off your hands.

(b) When you are on a stationary bike you cannot stay upright without putting your feet on the ground. However, when the bike is moving you have no trouble staying upright.

(c) Some magicians can jerk the tablecloth from under a dinner set including glasses, plates and cutlery, while leaving them at rest on the table.

2. A car with a mass equal to 2,000 kilograms decelerates from 30 metres per second to rest (0 metres per second) in a distance of 100 metres. Calculate the force required to stop the car.

3. State the reactions to the following actions:

(a) a tennis ball is hit by a racquet

(b) a horse walks along a road

(c) a man falls out of a tree

### Interactive Activities:

In order to make sure that you fully understand the concepts of Newton's laws, work through the online interactive activites given in the links below. You can complete these activities individually or in a group. However, make sure that you understand how Newton's laws work and how they relate to a real-life roller coaster. Remember, if you get stuck ask you teacher for help!

#### Activity 1: Newton's Laws

### Extra Materials and Videos:

Here are some extra links and youtube videos that may help you further understand Newton's Laws of motion. You can watch as many or as little as you like! Just make sure that you are able to understand the reasoning behind Newton's laws and can see how they apply to everyday life as well as in roller coaster physics

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