# Newtons Laws

## First Law

In essence, the object will continue to do what it was doing until something new happens to it.

**“An object will remain at a constant velocity until a new force acts upon it”**

The force that acts upon the object is called__ the resultant force.__

## Second Law

Newton’s second law is, perhaps, his most famous law.

**“The acceleration of an object is directly proportional to the resultant force exerted on it, and inversely proportional to its mass”**

a 𝛼 F and a 𝛼 1/m

In other words: Force = Mass x Acceleration

F = ma

- Force is measured in Newtons (N)
- Mass is measured in kilograms (kg)
- Acceleration is measured in metres per second squared (m/s
^{2})

## Weight

Weight is the **force acting on an object due to gravity.** The force of gravity close to the Earth is due to the gravitational field around the Earth.

The weight of an object is always considered to be acting at a **single point** referred to as the ‘**centre of mass**’.

The weight of an object is __directly proportional __to the mass.

To measure weight, you can use something called a N__ewton meter.__ As shown in the picture below, you hang your item on the hook and then read off the scale. There are different Newton meters for different weights, but they all work the same.

## Gravity

The equation for weight is one that you need to be able to recall and apply:

**Weight = Mass x Gravitational Field Strength**

W = m x g

- Weight is measured in newtons (N)
- Mass is measured in kilograms (kg)
- Gravitational Field Strength is measured in newtons per kilograms (N/kg)

In any calculation, you will always be given a value for g, the gravitational field strength (usually 9.8 or 10).

- A bus that accelerates at a rate of 0.5m/s2 when 5 people push it, each with a force of 750N, what is the mass of the bus?
- 7500kg
- A car accelerates at a rate of 5m/s^2. If it weighs 500kg how much driving force is the engine applying?
- 2500N
- A bus that accelerates at a rate of 0.5m/s^2 when 5 people push it, each with a force of 750N, what is the mass of the bus?
- 7500kg
- An object on Earth (g = 9.8N/kg) has a weight of 1252N, what is the mass of the object? Give you answer to 3 significant figures.
- 128kg
- Calculate the weight for an object which has a mass of 56kg. g = 9.8N/kg
- 548.8N