Mass:
Mass is the amount of substance in matter. Mass tends to
resist change in its state of rest or motion.
- Smaller mass = Easier to move and easier to stop
- Example: A ball at rest can easily be set in to motion by a gentle push and a rolling ball can easily be stopped by using a hand.
- Bigger mass = Harder to move and harder to stop
- Example: A parked truck cannot be set into motion unless and until a very large force is applied and a large force is needed to stop a moving truck.
Unit:
Mass is measured in g & kg. SI unit is kg.
Weight:
Weight of a body is defined as the action of gravity
on it. The greater the mass, the greater the weight and vice versa.
Weight = mass x acceleration due to gravity
w = mg
Unit:
Weight is measured in Newtons, symbol; N.
N = kgm/s2
w = mg where g is a constant; g = 10m/s2
so w is directly proportional to m.
Weight depends of acceleration due to gravity, if the
gravitational field is changed, the weight changes.
Example: 1kg weighs 10N on earth where g = 10m/s2
, but only 1.6N on moon where a = 1.6m/s2
Mass is independent of gravitational field and does not
change with change in gravitational fields.
Mass measuring balances:
- Precise/Accurate:
- A scientist in a lab or a gold seller uses precise balances to measure mass.
- Non-Precise:
- Vegetable or meat vendors use a normal balance to measure mass, as precision here is important, yet not vital.
Example:
If a gold seller sells you an extra 1g of gold on a purchase;
it will cause him a loss of $35, as gold is an expensive commodity costing
$35/g; but if a bag of 1kg of apples costs $2, the fruit vendor can give you an
extra 10g or so because that is affordable as apples only cost $0.002/g.
Therefore, precision is always important but in some cases, it is more vital
than others.
