Weight and Mass

What’s the Difference?

They’re the same.

• As long as you only ever live on the surface of the Earth….

So we use “mass” and “weight” interchangeably

• We shouldn’t. • We won’t any more in this class.• And it’s more confusing because we call these

“weights”. • We should really call them masses.• But we don’t…• English is barbaric • and irrational

GHOTI = FISH

• the gh = f as in rouGH• the o = i as in wOmen• the ti = sh as in naTIon

If you travel, the difference becomes very important

• Your mass doesn’t change (well, yes, if you lose or gain atoms). But basically, no.

• Your weight does change, depending where you stand.

If you had a mass of 1 kg

• On Earth, you’d press down on a scale with a FORCE of 9.81 N.

• F = m a• 9.81 N = 1 kg x 9.81 m/s/s

If you had a mass of 1 kg

• On the Moon, you’d press down on a scale with a FORCE of 9.81 N.

• F = m a• 1.62 N = 1 kg x 1.62 m/s/s

If you had a mass of 1 kg

• On Mars, you’d press down on a scale with a FORCE of 9.81 N.

• F = m a• 3.3 N = 1 kg x 3.3 m/s/s

If you had a mass of 1 kg

• In free fall (deep space, or orbiting the Earth), you’d press down on a scale with a FORCE of 0 N.

• F = m a• 0 N = 1 kg x 0 m/s/s

The interesting thing is, stuff still has MASS.

Therefore it still has INERTIA.The same amount as before.

As everywhere.So, your dead car is still going to

require the same effort to push to the mechanic.

Even though maybe it weighs a lot less.