Unit 1 General physics

Notes

  • The relationship between weight, mass and gravitational field strength can be expressed as:

    W=mg
    W = 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.
  • Example
    On 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

ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.

 
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