Headings Forces and
Motion Search Questions 
Mass, Weight and Gravity.
Mass
is an amount of substance. It is measured in kilograms.
It tells you how many particles
(atoms,
ions or molecules)
you have,
not what they weigh.
Gravity is a force of
attraction between masses.
Gravity is a property of mass,
the bigger the mass, the bigger the
gravity.
The further away from each other the
masses are,
the weaker
the gravity between them
(similar to the forces between
magnets and
charges,
except that gravity always attracts).
On Earth the force of
gravity is 10 N/kg.
The acceleration due to gravity
(how fast things accelerate when you drop them)
is 10 m/s2.
Weight is the force
of gravity pulling on a mass.
Weight is a force, and so it is
measured in Newtons, not kilograms.
Weight = mass x gravity
This equation is important!
Compare this with the general
formula F
= m
x a.
Weight is the force, gravity is the
acceleration.
If you go to the shops,
you will find fruit and vegetables weighed in kilograms.
In physics, this would be considered
to be wrong.
On Earth the force of gravity is
10 N/kg,
so you can convert mass into
weight by multiplying it by 10.
For example, 1kg of tomatoes weighs 10 N.
If you took your 1kg of tomatoes to
the moon,
you would still have the same mass
(the same number of tomatoes)
but they would weigh less
because the moon has less
gravity than the Earth.
People who sell tomatoes are
not generally troubled
by the difference between mass and weight,
since on the whole they do not try to sell tomatoes on
different planets.
Headings Forces and
Motion Search Questions
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