P1 Mass vs Weight Notes

Part 1

GRAVITY
& ORBITS

PART ONE:

MASS VS.
WEIGHT

https://www.youtube.com/watch?v=HG_Z1bKs6ow

*Mass = measure of amount
of matter in something (how
many molecules or particles in
something)

Quick review:

*Matter = anything that has
mass and takes up space

*Since the amount of
matter in something is the
same regardless of where it
is, mass is always the same
for that object

For example:

*A Pop-Tart has
mass and takes up space

*A Pop-Tart has a certain
amount of mass, and has
this same amount of mass
regardless of where it is
in the universe

Don’t confuse mass with weight!

* Mass does not depend
on the object’s location

* Weight is a measure of
the force of gravity pulling
on an object
(so location IS important!)

Your body has the same
mass on Earth and on
the moon…or
anywhere!

Your body has different
weights on Earth and
the moon...but why?

UNITS = N (newtons)

How to find WEIGHT:

W = m * g

WEIGHT = mass * gravity

How to find WEIGHT:

W = m * g

WEIGHT = mass * gravity

On Earth, gravity is
9.8 meters / sec 2

Remember to label

with N (for newtons) as your unit

​To make calculations easier, we will round this number to 10

Let’s practice!

Remember:

W = m * g (which we will round to 10)

1.

What is the weight on Earth of a cat with mass

of 3 kg?

~

Remember, these are estimations!

We are estimating gravity to be 10 m/s2,
not the accurate 9.8 m/s2 !

Poll

What is the estimated weight on Earth of a cat with mass
of 3 kg?

• 300N

• 30N

• 3N

Let’s practice!

Remember:

W = m * g

1.

What is the weight on Earth of a cat with mass

of 3 kg?

Poll

What is the weight on Earth of a cat with mass
of 3 kg?

• 29.4 N

• 30 N

Let’s practice!

Remember:

W = m * g (which we will round to 10)

~

2. What is the weight on Earth of a crate with mass

of 65 kg?

Remember, these are estimations!

We are estimating gravity to be 10 m/s2,
not the accurate 9.8 m/s2 !

Poll

What is the estimated weight on Earth of a crate with mass
of 65 kg?

• 650 N

• 6500 N

• 65 N

Let’s practice!

Remember:

W = m * g

2. What is the weight on Earth of a crate with mass

of 65 kg?

Poll

  What is the weight on Earth of a crate with mass
of 65 kg?

• 738 N

• 637 N

Let’s practice!

Remember:

W = m * g (which we will round to 10)

~

3. What is the weight on Earth of a person with mass

of 48 kg?

Remember, these are estimations!

We are estimating gravity to be 10 m/s2,
not the accurate 9.8 m/s2 !

Poll

What is the estimated weight on Earth of a person with mass
of 48 kg?

• 48 N

• 4800 N

• 480 N

Let’s practice!

Remember:

W = m * g

3. What is the weight on Earth of a person with mass

of 48 kg?

Poll

What is the weight on Earth of a person with mass
of 48 kg?

• 560.3 N

• 470.4 N

Review:

1. Gravity is a force of attraction between two objects.

2. Mass measures amount of “stuff” in an object, but

weight is the pull of gravity on object’s mass

3. Weight = mass x gravity and is measured in Newtons

4.

Acceleration due to gravity:

--9.8 m/s 2

--estimated value 10 m/s2