1. IP2.9.4 Motion under gravity - weight © Oxford University Press 2011 Motion under gravity - weight

2. IP2.9.4 Motion under gravity - weight © Oxford University Press 2011  When you drop an object it falls directly towards the ground.  It falls because of the gravitational attraction between the object and the earth. It is pulled by the force of the Earth’s gravitational field.  This force is called weight.  The weight of an object depends on two things:  its mass (the amount of matter) in kilograms (kg)  the gravitational field strength in newtons/kilogram (N/kg).

3. IP2.9.4 Motion under gravity - weight © Oxford University Press 2011 The equation linking weight, mass, and gravitational field strength is: weight of object = mass of object × gravitational field strength (newtons, N) (kilograms, kg) (newtons per kilogram, N/kg) The Earth’s gravitational field strength is about 10 N/kg.

4. IP2.9.4 Motion under gravity - weight © Oxford University Press 2011 If Dave has a mass of 90 kg what is his weight? Using: weight of object = mass of object × gravitational field strength (newtons, N) (kilograms, kg) (newtons per kilogram, N/kg) Dave’s weight is 90 × 10 = 900 N

5. IP2.9.4 Motion under gravity - weight © Oxford University Press 2011  Remember that in everyday usage the term ‘weight’ is actually used to mean ‘mass’.  Normally people would say Dave weighs 90 kg when actually his mass is 90 kg and he weighs 900 N.  Make sure you know the difference between the two and use them correctly.