Mass, Weight & Gravity overview
In this unit, we will be examine the difference between mass, weight and gravity, and how inertia, mass and distance plays a role.
When I am finished with mass, weight & gravity, I Can...


Part 1: Direction of Gravity


Part 2: Factors (variables) that affect gravitational attraction
Atoms gives us matter. Matter gives us mass. Matter/mass gives the object gravity. Being next to a planet that has a HUGE amount of matter/mass, which also has gravity, is what gives us weight. In this section, we examine how different scenarios affect your weight.
 Mass & Distance affect the gravitational forces / attraction (aka  weight) between two objects.
 Because you are made of matter, you exert gravitational fields. The planet is also made out of matter  and it too exerts gravitational fields. This is why you are attracted to the planet. This is why you squish a bathroom scale when you stand on it.
 Gravity is relatively a very weak force. You have to be next to a planet sized object in order to even start to sense gravity.
Below are three ways to affect the gravitational attraction (aka: weight) between you and the planet.
Increasing or decreasing your mass
Lab Activity Test 1

Increasing or decreasing the planets mass
Hypothetical Test 2

Increasing or decreasing the distance between you and the planet
 If you increase your distance from the planet, your weight goes down  even though your mass stays the same. (Remember  mass is the amount of matter an object  such as you  has).
 The closer you get to the planet  your weight goes up  even though your mass stays the same.
 (The distance must be considerably distant from the planet. The astronauts you see in space are much closer to the earth than you think  and are technically not weightless  but feel weightless because they are falling towards the earth as they travel sideways).
Lab Activity Test 3

Lab Activity Test 2

Hypothetical Test 2
The Relationship Between Gravity, Mass & Distance
Your weight is a measure of the pull of gravity between you and the body you are standing on. This force of gravity depends on a few things. First, it depends on your mass and the mass of the planet you are standing on. If you double your mass, gravity pulls on you twice as hard. If the planet you are standing on is twice as massive, gravity also pulls on you twice as hard. On the other hand, the farther you are from the center of the planet, the weaker the pull between the planet and your body. The force gets weaker quite rapidly. If you double your distance from the planet, the force is onefourth. If you triple your separation, the force drops to oneninth. Ten times the distance, onehundredth the force. See the pattern? The force drops off with the square of the distance. If we put this into an equation it would look like this:
The two "M's" on top are your mass and the planet's mass. The "r" below is the distance from the center of the planet. The masses are in the numerator because the force gets bigger if they get bigger. The distance is in the denominator because the force gets smaller when the distance gets bigger. Note that the force never becomes zero no matter how far you travel. (Exploratorium). To the side is a short video explaining this equation and the variables associated with the force of gravity, and below is a diagram which the equation refers to. 

Part 3: Gravity and Acceleration
 In deep space, there is very little acceleration because the distance between you and the next available planet minimizes the gravitational force acting on you. (technically  there is still gravity  but that all depends on the distance between you and the next available planet, star or moon. Here's more to help you understand).
 On the moon, because there is little mass, there is little gravity  therefore, little acceleration (see section 2).
 On Jupiter, because there is a LOT of mass, there is a LOT of gravitational attraction  therefore, a LOT of acceleration (again, see section 2).

Go to about 5 minutes.

Part 4: Falling Objects in Gravity Fields
 All objects fall at the same rate of acceleration  so long as there is no air resistance.
On this day  we examine the question: "Do all objects fall at the same rate?" If they do not  what factors influence the rate of decent?
Part 4: Lab 1  Density Cube set

Part 4: Lab 25  Dropping different balls

What we found was that each of the density cubes hit the ground at the same time  no matter what the mass. But, we did find that the crumpled paper and flat paper hit the floor at different times. Could it be that different masses are not a factor? YES! Mass does not make a difference. That's because of inertia. As the object increases its mass, it also increases its gravitational force (i.e. weight). Simultaneously, it has also increased its inertia, or resistance to the push/pull/force) And that's why all masses fall at the same rate.
To further and confirm our findings, when we drop the basket ball, bouncy ball and bowling ball  they all hit the ground at the same time.
However, could air resistance be a factor? YES! When we dropped the crumpled paper and compared it to the flat paper  the crumpled up paper hit the ground first by a long shot. It was also confirmed when we dropped the heavier beach ball to the lighter tennis ball  and the tennis ball won. This is because these objects have to swim through the air molecules as they drop. We call this wind resistance (or rather  friction with air).
Therefore, when you remove the air  at such places such as the moon  where there is no atmosphere, light objects (such as a feather) fall equally as fast as heavier objects (like a hammer). (See the two videos below  followed by the misconception videos below).
To further and confirm our findings, when we drop the basket ball, bouncy ball and bowling ball  they all hit the ground at the same time.
However, could air resistance be a factor? YES! When we dropped the crumpled paper and compared it to the flat paper  the crumpled up paper hit the ground first by a long shot. It was also confirmed when we dropped the heavier beach ball to the lighter tennis ball  and the tennis ball won. This is because these objects have to swim through the air molecules as they drop. We call this wind resistance (or rather  friction with air).
Therefore, when you remove the air  at such places such as the moon  where there is no atmosphere, light objects (such as a feather) fall equally as fast as heavier objects (like a hammer). (See the two videos below  followed by the misconception videos below).
Additional videos about falling objects




Part 5: Mass v. Weight
 Mass & Weight are two different things.
 Mass: the amount of matter in an object.
 Weight: the force of gravity on an object (1st object w/ mass) near the surface of a planet (2nd object w/ mass).
 Weight is a force. Mass is not.
 In order to sense weight, you have to be near a second planet sized object that has a lot of mass. (See part 2)

 Spring Scales (Bathroom Scales and other force meters) measures forces. The springs either squish or stretch (depending on how it is set up) in response to the forces acting on it. This measures the level of attraction between you and the planet you are sitting on. This is why you weigh much less in space, but still have mass. This is also why you weigh less on the moon and more on Jupiter.
The idea thus far...
Weight, or the gravitational attraction between two objects with mass, is influenced by two factors: the amount of matter an object has (mass) and the distance between them.
While here on earth, when you increase your mass, you simultaneously increase your gravitational pull. As a result, you are more attracted to the earth  this is why as you get larger  you simultaneously increase your weight, or gravitational force between you and the earth.
IOW: If one of the objects increases its mass, it increases its gravitational pull. If you increase the distance between you and the object, the force of gravity decreases and so does your weight.
Check out this source: Jefferson Lab
The video below also helps to explain the difference between mass and weight. I would highly encourage you to watch it.
While here on earth, when you increase your mass, you simultaneously increase your gravitational pull. As a result, you are more attracted to the earth  this is why as you get larger  you simultaneously increase your weight, or gravitational force between you and the earth.
IOW: If one of the objects increases its mass, it increases its gravitational pull. If you increase the distance between you and the object, the force of gravity decreases and so does your weight.
Check out this source: Jefferson Lab
The video below also helps to explain the difference between mass and weight. I would highly encourage you to watch it.
Part 6: Weight is a Force
Since a force is a push or pull, when you are attracted to the earth, the earth's gravity pulls on you and causes you to accelerate towards the ground  hence the phrase  the pull of gravity. Therefore, weight is a measurement of the attractive forces between you and the earth  and mass, once again, is simply the "stuff" or "atoms" that make you up.
 Force is equal to Mass x Acceleration (F=MA)
 Weight is equal to Mass x Acceleration rate of gravity (W=MG)
 Therefore, weight is a force.
Part 7: Inertia  motion in space


Part 8: Acceleration rate of the Earth
In an earlier lab  we learned that all objects fall at the same rate. In today's lab  we are examining the acceleration rate of the earth by measuring the height and dropping a golf ball over the edge and timing how long it takes to drop it. To do this  we:
 Took a piece of string with a plumb bob at the end and hung it over the side of the balcony to measure its height.
 Took a golf ball and dropped it off over the edge and timed how long it took to hit the bottom.
 Recorded our data and repeated the process at least 5 times.
 Took an average of the time and plugged this information into the following equation:
By dropping an object over the balcony & timing it  students calculate the acceleration rate of the Earth.
Here is the data of some students that got it the closest.
Height: 5.74 meters
Time: 1.08 seconds
Here is the data of some students that got it the closest.
Height: 5.74 meters
Time: 1.08 seconds
Step 1: Drop the string down the balcony (So that you can measure the height you will drop the object).
Step 2: Measure the string (So that you can measure the height you will drop the object  [5.74 m]).
Step 3: Drop the object over the balcony (Look at the ball of clay as it descends down).
Step 4: Time how long it takes to descend (1.8 seconds).
Step 5: Record your data. Use this information to determine the rate of acceleration.
Wrapping it all up:

