Mass, Weight and Gravity

In I/GCSE Physics, the building block of all forces and thus motion: **Mass**. The first thing to clarify is a very common misconception – **Mass and Weight are not the same thing! **This is unfathomably important to remember:

**Mass**is a universal value which is measured in**Kilograms**and**does not change depending on the forces acting**upon it.**Weight**is most commonly a planetary confined value that**does change depending on the Gravitational Field**acting upon it. Weight is also measured in Kilograms... You can see how this will be annoying, just always look for Weight or Mass.

So, how do we calculate weight in I/GCSE Physics?

In order to do that we are going to have to understand a little more about **Forces**: a Force acts as a **push or pull on an object**, whether that be away from or towards the object applying the Force. The Earth has a **Gravitational Field Strength (GFS)** of **10N **or** ten Newtons**, meaning that the Earth’s Gravitational Field will apply ten **Newtons of force** on an object, in this case it will be a pulling Force; this is what we must know in order to calculate weight on earth.

**Weight** is relative to a planet’s** Gravitational Field**. Meaning, the same object will have a different weight depending on the **GFS** of the planet. Let’s calculate it: we know that the **GFS of Earth is 10N,** meaning that for every one **kg** of mass there will be **10N of Force**. Hence, we must times our **Mass** by 10 in order to calculate our **Weight** on Earth.

**Example**

Say we have an object with a mass of **2kg**, what would it weigh on Earth?

1. All we must do is **multiply it by 10** and we have the Weight on Earth; **2 × 10 = 20**.

2. Therefore, our object weighs **20kg** on Earth.

Challenge:

a) The GFS of the moon is **1.6**, find how much you would weigh on the moon?

b) Find how much you would weigh in space (your Mass).

**Formula for Weight: W = mg (Weight = Mass × GFS)**

*N.B. ‘ g’ ≠ Gravity! If you state this in the exam you will be marked down! ‘g’ = Gravitational Field Strength.*

End of this topic!