Unit 1 General physics
Notes
The relationship between weight, mass and gravitational field strength can be expressed as:
W=mgW = weight (N) m = mass (kg) g = gravitational field strength (N/kg)  On Earth the gravitational field strength is 10N/kg.
 Because g is a constant near to Earth, the weight of an object is proportional to its mass.
 If mass doubles, weight doubles. It follows that weights may be compared using a mass balance.

ExampleOn Earth a man has a mass of 85kg. Calculate his weight.
Step 1 List all the information in symbol form and change into appropriate and consistent SI units if required.
m=85kg
g=10N/kg
W=?
Step 2 Use the correct formula.
W=mg
Step 3 Calculate the answer by putting the numbers into the formula.
W=mg=85 × 10=850N
W = mg = 85 × 10 = 850N
ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.