Download Gravity-mod

Level 7 & 8
Describe how gravity affects people and things on earth, the moon and other planets.
Level 9 & 10
Explain the relationship between gravity and the mass of an object and the link between gravity and orbits
What is gravity?
What is gravity?
• Gravity is a force pulling together all matter (which is anything you can physically
touch)
• Mass is how we measure the amount of matter in something.
• The more massive (bigger) something is, the more of a gravitational pull it exerts. As
we walk on the surface of the Earth, it pulls on us, and we pull back. The Earth pulls
harder so we can’t affect it, but it can make us fall over.
• Gravity also depends on how far you are from something. This is why we are stuck
to the surface of the Earth instead of being pulled off into the Sun, which has many
more times the gravity of the Earth.
TAKE HOME POINTS
Gravity:
-force that pulls together all matter
-depends on both the mass of an object and the distance from the
object
E.g. The gravity exerted on us from the Earth is far greater than that
exerted on us by the sun even though the sun is far bigger
What is gravity?
Weight and Mass
What's the difference between weight and mass?
Mass is a measurement of how much matter is in an object; weight is a measurement of how hard gravity is pulling on
that object.
2.5 Kg
We
measure
weight in N
We
measure
mass in Kg
A. Gravity and Air Resistance
B. Gravitational pull, free fall, weightlessness
C. Center of Gravity of an object
A. Gravity and Air Resistance
Gravity and Air Resistance: Experiment 1 Book and paper
If you drop a book and a flat piece of paper from the same
height, which would hit the ground first and why?
Experiment:
1. Hold the book in one hand and the paper in the other.
2. Hold both objects high in front of you at equal heights.
3. Release both objects at the same time.
Questions:
• Who thinks the book will hit the floor first?
• Who thinks the paper will hit the floor first?
• Who thinks both objects will hit the floor at the same time?
Observation: When dropped separately the book hits the
floor first. When dropped together they fall together, as
the sheet does not experience the same air resistance
when it is dropped together with the book.
Explanation: Because of the paper's shape, its fall is
slowed by air pushing up against its under-surface – this
slowing effect is called air resistance.
A. Gravity and Air Resistance
Gravity and Air Resistance: Experiment 2 Different balls
If you drop balls of the same size but made of different
materials, which ball would hit the ground first and why?
Experiment:
1. Hold two balls of similar size, one in each hand.
2. Hold both objects high in front of you at equal heights.
3. Release both objects at the same time.
Questions:
• Which ball do you think will hit the floor first?
• OR Do you think they will hit the floor at the same time?
Observation: Both balls hit at roughly the same time.
Explanation: If you neglect air resistance, objects falling
near Earth’s surface fall with the same approximate
acceleration 9.8 meters per second squared (9.8 m/s2, or
g) due to Earth's gravity.
All objects fall at the same rate, regardless of their mass
How fast something falls isn't dependant on the mass of
the object. Acceleration due to gravity is a constant
regardless of the mass of the object.
The force at which the object hits the ground is
dependant on the mass but not how fast those objects
fall, as this is a constant – gravity causes the same
acceleration for everything
Galileo’s predecessors….
Girolamo Borro 1575 (taught Philosophy in Pisa when Galileo was a student there)
- Borro threw two balls at the same time from the highest window of his house; the
balls had the same weight, but were made from different materials (wood vs. lead)
- He observed that the wooden ball fell faster and hit the ground first.
Giuseppe Moletti 1576
- Moletti released, from a high tower, a lead ball of 20 pounds together with a lead
ball of 1 pound; in another experiment, he released a wooden ball together with a
same-sized lead ball. In both cases, the two balls were observed reaching the ground
at the same time.
Simon Stevin and Jan Cornets de Groot
- They simultaneously dropped two balls, one 10 times as heavy as the other, from a
height of 30 feet onto a wooden platform.
- In one experiment, the balls were made of the same material (lead); in another, they
were the same size.
- In both experiments, the two balls hit the platform at precisely the same moment.
What would happen if you did these
experiments in a vacuum?
This kind of vacuum!
I can’t get
inside Henry
the vacuum!!!
When an object falls with air resistance, both its acceleration and speed change during its motion. When an object falls in a
vacuum, there is no air resistance because there is no air in a vacuum.
B. Gravitational pull, free fall, weightlessness
Polystyrene cup with hole in side, water, tupperware container
• when you held the cup still and uncovered the hole did the water flow out of it?
• when you dropped the cup did the water flow out the hole?
Answer the questions about your observations and use the internet to help explain them
C. Center of Gravity of an object
1. Coke can with 100 mL water
2. Glass, toothpick, fork, spoon and matches
3. Hammer, ruler and string
The two forks are balanced on the edge of the
glass by a toothpick.
Weight changes, mass doesn’t!
I’m always going to be 1,000Kg
No matter where I am!
But my weight (force) can change
when the force of gravity changes.
Unless he eats me! then his mass will
increase!
Weight a minute…
Weight is a measurement of force…
Force is always measured in Newtons (N)
Weight (N) = Mass (Kg) X Acceleration of Gravity
What’s my weight?
(in Newtons!)
Mass = 1000Kg
Acceleration of
gravity: 9.8 m/s
Is there gravity in space?
There is gravity everywhere. Gravity from the Sun reaches
throughout the solar system and beyond, keeping the
planets in their orbits. Gravity from Earth keeps the Moon
and human-made satellites in orbit.
It is true that gravity decreases with distance, so it is
possible to be far away from a planet or star and feel less
gravity.
http://www.qrg.northwestern.edu/projects/vss/docs/s
pace-environment/1-is-there-gravity-in-space.html
Why do astronauts feel weightless in space?
The reason that astronauts feel weightless is not to do
with their being no gravity (‘cos there is) but actually
has to do with their position compared to their
spaceship.
We feel weight on Earth because gravity is pulling us
down, while the floor or ground stop us from falling.
We are pressed against it. Any ship in orbit around the
Earth is falling slowly to Earth.
Since the ship and the astronauts are falling at the
same speed, the astronauts don't press against
anything, so they feel weightless.
What is an orbit?
An orbit is a regular, repeating path that an object in space takes around another one. An object in an orbit is called a
satellite. A satellite can be natural, like the moon, or human (or extraterrestrial?) -made.
• In our solar system, the Earth orbits the Sun, as do the other eight planets.
• They all travel on or near the orbital plane, an imaginary disk-shaped surface in space.
• All of the orbits are circular or elliptical in their shape.
• In addition to the planets' orbits, many planets have moons which are in orbit around them.
What causes an orbit to happen?
Orbits are the result of a perfect balance between the forward motion of a body in space, such as a planet or moon, and
the pull of gravity on it from another body in space, such as a large planet or star. An object with a lot of mass goes
forward and wants to keep going forward; however, the gravity of another body in space pulls it in. There is a continuous
tug-of-war between the one object wanting to go forward and away and the other wanting to pull it in.
These forces of inertia and gravity have to be perfectly balanced for an orbit to happen. If the forward movement (inertia) of one
object is too strong, the object will speed past the other one and not enter orbit. If inertia or momentum is much weaker than
the pull of gravity, the object will be pulled into the other one completely and crash.
http://www.qrg.northwestern.edu/projects/vss/docs/sp
ace-environment/1-what-causes-an-orbit.html
http://www.qrg.northwestern.edu/projects/vss/docs/sp
ace-environment/1-what-travels-in-an-orbit.html
• What travels in an orbit?
• Almost all of our neighbors in space are in orbit around something:
• All of the planets are in a circular or elliptical orbit around the Sun.
• Our moon and the moons of the other planets are in orbit around their planets.
• Comets are in an irregular orbit around the Sun.
• Most asteroids in our solar systems are orbiting the Sun in a band between Mars and Jupiter. Most humanmade spacecraft in space are orbiting Earth. itational center for the other stars in the Milky Way. They travel
around the center of the Milky Way as our planets go around the Sun.
• There are a few things that we are familiar with, though, that aren't in orbits. When a meteorite enters our
atmosphere and becomes a "shooting star," it is no longer in an orbit. Some space probes like Voyager have
achieved escape velocity and broken away from the pull of the Sun's gravity and left the solar system. These
space probes are not in orbit around a planet or the Sun, or they would stay near a planet or continue in a
loop around the Sun.
Who orbits who?
Draw the sun, moon, Earth and the satellite in the correct orbit.
Planet Earth orbits the sun over 365 days
The moon orbits planet Earth over 27 days
The satellite orbits planet Earth (depends on type of satellite)
Complete worksheets from last lesson
• Should have one of two worksheets – harder and easier
• Please ask for help when needed