1. Gravity

2. Lesson1: Gravity Lesson Objectives: Describe what Gravity is
Describe how Gravity varies with Mass and Distance

3. Gravity Luke – I am your Father!
I just know this is really what astronauts are thinking
when they are floating around out there!

4. Gravity PULLS all objects
- Friction and Gravity
Main Concept #1:
Gravity is the “attractive force” between all objects in the universe.
Gravity PULLS all objects
towards it’s source!
Use the magnets as a demo.

5. Gravity is what makes all objects in our universe come together!
As you watch notice that all the objects with
mass are being pulled to the source
of gravity.
Source of Gravity
Also; notice that the new object being created
around the source of gravity is growing larger
Basically, this is how we think planets are eventually formed!

6. Main Concept #2: Gravity is what effects all of the motion in space.
Would any of the planets orbit the sun if the sun had no gravity?

7. Law of Gravity Mass & Distance
- Friction and Gravity
Law of Gravity
Gravity PULLS all objects
towards it’s source!
The source of gravity is almost
always right in the middle
This is why all objects in the
universe have a “round” shape!
Main Concept #3: There are two factors that effect the force of gravity:
Mass & Distance
Use the magnets as a demo.

8. Main Concepts of Gravity: Effect of Mass
Everything with mass has gravity
MORE MASS = MORE GRAVITY!!!
LESS MASS = LESS GRAVITY!!!
So, which of these two planets
would have more gravity?

9. Effect of Mass on Gravity:
The more planet’s mass…the more its gravity effects you!
Gravity pulls everything
towards its source!
The source of gravity
for us is in the “core”
(centre) of the Earth!
No matter where you are on the planet, the pull is the same. This
is why “down”
is always at your feet!

10. Planet Mass & Gravity
Jupiter (the largest planet in our solar system) has way more mass than our tiny little planet.
Therefore it has a lot more gravity!!!

11. Laws of Gravity: Distance
The closer you are to the object, the more your going to feel the effects of gravity.
The farther you are from the object, the less your going to feel the effects of gravity.

12. Distance from the center of Gravity matters!
No Difference
Let’s see how distance from the center plays a major roll in your weight.
Huge Difference
These two people are the same distance from the center of the earth, therefore, the pull of gravity is the same!
Let’s see what happens when we get farther away.
This is also why satellites can orbit
around the planet.
As the Astronaut gets farther away,
The effects of Earth’s gravitational pull is less,
so you can “float" around! The astronaut weighs less!

13. Jupiter has more mass than Earth; Therefore it has more gravity
Conclusion
Gravity is dependent upon the mass of two objects and the distance between them.
If mass increases – Force of Gravity increases
If distance increases – Force of Gravity decreases.
Jupiter has more mass than Earth;
Therefore it has more gravity
The satellite is farther from the center of Earth than we are;
Therefore the satellite “feels” less pull of gravity

15. Lesson 2: Gravitational Field Strength
Lesson Objectives
State the value of g on Earth and on the moon
Describe the difference between Mass and Weight

16. ‘g’ on the Earth and Moon
On Earth the gravitational field strength ‘g’ is 10N/kg. This is the force that acts on 1kg in the Earth’s gravitational field.
Gravitational field strength ‘g’ is different on other planets, on moons and on stars. Your weight would be different on different planets because ‘g’ would be different.
The Apollo astronauts could jump much higher on the Moon because ‘g’ on the Moon is 1.6N/kg. Their weight decreased as they moved away from the Earth.

17. Amount of MATTER in an object.
Mass
Amount of MATTER in an object.
Not to scale
4 kg
0.1 kg
Measured in kilograms (kg).
Stays the same anywhere you go.

18. On Earth On Moon A downward-pulling force on an object due to gravity.
Weight
A downward-pulling force on an object due to gravity.
Measured in Newtons (N)
Changes depending on where you are.
On Earth On Moon

19. Experiment: Gravity Cups
Station
Mass (g)
Mass (kg)
Weight (N) A B C D

20. Imagine travelling around the Solar System with a container of food
Imagine travelling around the Solar System with a container of food. You don’t open the container but its weight changes on the Moon and on different planets. If gravity is stronger, the container feels heavier. If gravity is weaker, the container feels lighter.
1 In your table, write the mass of the container that is shown on the lid. Mass is measured in kg. It does not change.
2 Weigh the food container that is at each station using a newtonmeter. Weight is measured in newtons. It does change if gravity changes.
3 Write the weight of the container and station name in your table.
4 Work out the gravity felt by the container in each station. This is called the gravitational field strength, g.
5 Use the data table to decide where you were when you visited each station.

21. Gravity is strongest on Jupiter. It is weakest on the Moon
Gravity is strongest on Jupiter. It is weakest on the Moon. Look at your results.
1Which station shows what the container weighs on Jupiter?
2 Which station shows what the container weighs on the Moon?
3 Write down the name of the place or places where the container weighs less than on Earth.
4 Write down the name of the place or places where the container weighs more than on Earth.

22. Answers
1 Station A = 1.7 N/kg; Station B = 27 N/kg; Station C = 3.8 N/kg; Station D = 12 N/kg
2 Assuming the same measurements are used as given in the technician notes, Station A: Moon, Station B: Jupiter, Station C: Mars, Station D: Saturn.
3 Weight is how hard gravity pulls on a mass. It changes in different places. weight = mass × gravitational field strength
4 Mass is how much matter something is made from (the amount of particles). It doesn’t change in different places.

23. Homework!
Gravity and weight
Worksheet

24. Lesson 3: Your weight on different planets
Lesson Objectives
Calculating your weight on different planets

26. Calculating Weight and Mass
In order to calculate mass or weight of an object you need the gravitational field strength.
On Earth it is approx 10 N/kg
Weight = mass x gravitational field strength
(N) (kg) (N/kg)
You need to remember this!!

27. REMEMBER the gravitational force strength is 10N/kg on Earth.W g M
REMEMBER the gravitational force strength is 10N/kg on Earth.
Calculate the mass of a book which has a weight of 10N.
Calculate the mass of a man who has a weight of 750N.
What is the weight of a pushchair which has a mass of 7kg?