Highlight the main ideas. Summarize these main ideas in one or two paragraphs
Gravity is a force that attracts all objects towards each other. Gravitational attraction is
greater for more massive objects.
Gravity is a force that attracts all objects towards each other. Gravitational attraction is
greater for more massive objects.
Gravity decreases as distance between the objects increases.
Every object in the Universe is being attracted towards every other object by the force of gravity.
Gravity keeps people on the Earth’s surface.
Gravity keeps people on the Earth’s surface.
Gravity keeps the International Space Station in orbit around the Earth.
Gravity keeps the Moon orbiting around the Earth.
Gravity keeps the Earth orbiting around the Sun.Isaac
Newton was the first to come up with the idea that all objects are attracted towards
each other by gravity.
Newton was the first to come up with the idea that all objects are attracted towards
each other by gravity.
The Moon is 360,000 km from the Earth and only needs to be travelling at 1 km/s to stay in
orbit around the Earth. Any two masses are attracted towards each other by gravity.
This force of gravity causes the Moon to change direction to make it orbit around the Earth.
Gravity doesn’t disappear just because you are above the atmosphere.
Isaac Newton worked out that, if the distance from the centre of the Earth doubles,
gravity becomes a quarter as much as it was on the surface.
As a satellite moves around the Earth in a circular orbit,
the direction of the force of gravity is always towards the centre of the Earth.However
, if the satellite is given speed in any direction horizontal to the surface of the Earth,
it will travel further before it hits the Earth. If it is given enough speed, it will travel so far that,
as it curves towards the Earth, it will miss the Earth altogether.
orbit around the Earth. Any two masses are attracted towards each other by gravity.
This force of gravity causes the Moon to change direction to make it orbit around the Earth.
Gravity doesn’t disappear just because you are above the atmosphere.
Isaac Newton worked out that, if the distance from the centre of the Earth doubles,
gravity becomes a quarter as much as it was on the surface.
As a satellite moves around the Earth in a circular orbit,
the direction of the force of gravity is always towards the centre of the Earth.However
, if the satellite is given speed in any direction horizontal to the surface of the Earth,
it will travel further before it hits the Earth. If it is given enough speed, it will travel so far that,
as it curves towards the Earth, it will miss the Earth altogether.
Close to the Earth at an altitude of 100 km, a satellite needs to be moving at 8 kilometres
per second (28 000 km/h) to stay in orbit. Close to the Earth at an altitude of 100 km, a satellite
needs to be moving at 8 kilometres per second (28 000 km/h) to stay in orbit.
Astronauts appear to be weightless for the same reason that a person
on a trampoline feels weightless when in the air.
per second (28 000 km/h) to stay in orbit. Close to the Earth at an altitude of 100 km, a satellite
needs to be moving at 8 kilometres per second (28 000 km/h) to stay in orbit.
Astronauts appear to be weightless for the same reason that a person
on a trampoline feels weightless when in the air.
When does gravity decrease? Gravity decreases as the distance between the objects increases.
When does the force of gravity become noticeable? Gravity only becomes noticeable if one or both
of the objects has a lot of mass, such as the Earth.
of the objects has a lot of mass, such as the Earth.
Gravity disappears when you are above the atmosphere. True or False? It is true that gravity
disappears when you are above the atmosphere.
disappears when you are above the atmosphere.
According to the text, how long does it take the International Space Station (ISS) to orbit Earth?
It takes about 90
minutes for ISS to orbit Earth.
It takes about 90
minutes for ISS to orbit Earth.
Who first stated that all objects are attracted towards each other by gravity? Isaac Newton
first stated that all objects are attracted towards each other by gravity.
first stated that all objects are attracted towards each other by gravity.
Find six words in the text that have a suffix. Noticeable, weightless, pulling, accepted,
horizontally, gravitation
horizontally, gravitation
Gravity
Gravity is a force that attracts all objects towards each other. People are attracted towards
the Earth and the Earth towards people, the Moon and the Earth are attracted towards each
other, and the Sun and the Earth are attracted towards each other. All of these attractions
are caused by gravity. Gravitational attraction is greater for more massive objects. Gravity
decreases as distance between the objects increases.
Gravity attracts all things towards each other
Every object in the Universe is being attracted towards every other object by the force of gravity. This
means that there is nowhere you can go in the Universe where gravity is not acting. Examples of gravity
in action:
means that there is nowhere you can go in the Universe where gravity is not acting. Examples of gravity
in action:
Gravity holds the atmosphere in place around the Earth.
Gravity keeps people on the Earth’s surface.
Gravity keeps the International Space Station in orbit around the Earth.
Gravity keeps the Moon orbiting around the Earth.
Gravity keeps the Earth orbiting around the Sun.
Isaac Newton was the first to come up with the idea that all objects are attracted towards each other
by gravity. Even people are attracted towards each other by gravity, but this force is so small that it is
not noticeable. Gravity only becomes noticeable if one (or both) of the objects has a lot of mass, such
as the Earth. Close to the Earth at an altitude of 100 km, a satellite needs to be moving at 8 kilometres
per second (28 000 km/h) to stay in orbit. The Moon is 360,000 km from the Earth and only needs to be
travelling at 1 km/s to stay in orbit around the Earth.
by gravity. Even people are attracted towards each other by gravity, but this force is so small that it is
not noticeable. Gravity only becomes noticeable if one (or both) of the objects has a lot of mass, such
as the Earth. Close to the Earth at an altitude of 100 km, a satellite needs to be moving at 8 kilometres
per second (28 000 km/h) to stay in orbit. The Moon is 360,000 km from the Earth and only needs to be
travelling at 1 km/s to stay in orbit around the Earth.
There is gravity in space
Earth-Moon system and gravity
Any two masses are attracted towards each other by gravity. This force of gravity causes
the Moon to change direction to make it orbit around the Earth.
the Moon to change direction to make it orbit around the Earth.
Gravity doesn’t disappear just because you are above the atmosphere. Even if an object is high above
the Earth’s atmosphere, there will still be a strong force of gravity pulling it towards the centre of the
Earth. At an altitude of 30 km, you would be above 99% of the Earth’s atmosphere. At 100 km, you
would officially be in space, yet the weight force of gravity would still be nearly the same.
You and the Earth would still be pulled together.
the Earth’s atmosphere, there will still be a strong force of gravity pulling it towards the centre of the
Earth. At an altitude of 30 km, you would be above 99% of the Earth’s atmosphere. At 100 km, you
would officially be in space, yet the weight force of gravity would still be nearly the same.
You and the Earth would still be pulled together.
Isaac Newton worked out that, if the distance from the centre of the Earth doubles,
gravity becomes a quarter as much as it was on the surface.
A satellite with a mass of 1000 kg has a weight force of 9800 N at the Earth’s surface.
The radius of the Earth is about 6366 km, so at 6366 km above the Earth’s surface,
the distance from the centre of the Earth will have doubled.
The weight force pulling it towards the centre of the Earth will now only be a quarter as much
but will still be 2450 N.
gravity becomes a quarter as much as it was on the surface.
A satellite with a mass of 1000 kg has a weight force of 9800 N at the Earth’s surface.
The radius of the Earth is about 6366 km, so at 6366 km above the Earth’s surface,
the distance from the centre of the Earth will have doubled.
The weight force pulling it towards the centre of the Earth will now only be a quarter as much
but will still be 2450 N.
So why doesn’t a 1000 kg satellite just fall back to Earth?
Sideways speed keeps satellites in orbit.
As a satellite moves around the Earth in a circular orbit, the direction of the force
of gravity is always towards the centre of the Earth.
of gravity is always towards the centre of the Earth.
At an altitude of 100 km, you would be so high that you would see black sky and stars
if you looked upwards. If you took a satellite to this height and released it, it would still fall towards
the Earth because the force of gravity is nearly the same as it is at the Earth’s surface.
if you looked upwards. If you took a satellite to this height and released it, it would still fall towards
the Earth because the force of gravity is nearly the same as it is at the Earth’s surface.
However, if the satellite is given speed in any direction horizontal to the surface of the Earth,
it will travel further before it hits the Earth. If it is given enough speed, it will travel so far that,
as it curves towards the Earth, it will miss the Earth altogether.
At just the right speed, it will move around the Earth in a circular motion.
This type of motion and the path that a satellite moves in is called an orbit.
it will travel further before it hits the Earth. If it is given enough speed, it will travel so far that,
as it curves towards the Earth, it will miss the Earth altogether.
At just the right speed, it will move around the Earth in a circular motion.
This type of motion and the path that a satellite moves in is called an orbit.
Close to the Earth at an altitude of 100 km, a satellite needs to be
moving at 8 kilometres per second (28 000 km/h) to stay in orbit. At higher altitudes, satellites
do not need to be travelling as fast. Television communication satellites are at a higher altitude
of 36 000 km and only need to travel at 3 km/s (11,000 km/h).
moving at 8 kilometres per second (28 000 km/h) to stay in orbit. At higher altitudes, satellites
do not need to be travelling as fast. Television communication satellites are at a higher altitude
of 36 000 km and only need to travel at 3 km/s (11,000 km/h).
The Moon is 360,000 km from the Earth and only needs to be travelling at 1 km/s to stay in
orbit around the Earth.
orbit around the Earth.
If there is gravity in space, why do astronauts appear weightless?
Astronauts appear to be weightless for the same reason that a person on a trampoline
feels weightless when in the air. There is still the same amount of gravity acting, but there is
no floor pushing upwards on the astronaut, so the weight force cannot be felt.
feels weightless when in the air. There is still the same amount of gravity acting, but there is
no floor pushing upwards on the astronaut, so the weight force cannot be felt.
If a person was in an elevator and the cables broke and the brakes failed (we are assured this
cannot happen), the person and the elevator would fall towards the Earth at the same rate.
The floor would not be holding the person upwards, so the person could enjoy the sensation of
weightlessness (for a brief while).
cannot happen), the person and the elevator would fall towards the Earth at the same rate.
The floor would not be holding the person upwards, so the person could enjoy the sensation of
weightlessness (for a brief while).
This is the same for astronauts high above the atmosphere on the International Space Station
(ISS) at an altitude of about 400 km. Gravity is still strong, but the astronaut and the ISS fall towards
the ground at the same rate. They are also both travelling horizontally at 28,000 km/h.
As they fall towards the ground, they travel so fast horizontally that they miss the Earth
altogether and orbit the Earth once every 90 minutes.
(ISS) at an altitude of about 400 km. Gravity is still strong, but the astronaut and the ISS fall towards
the ground at the same rate. They are also both travelling horizontally at 28,000 km/h.
As they fall towards the ground, they travel so fast horizontally that they miss the Earth
altogether and orbit the Earth once every 90 minutes.
Nature of science
Science ideas change over time. Isaac Newton’s gravity-based world view has since been
superseded by Albert Einstein’s ideas that all masses distort space and time.
This highlights the fact that science is not a fixed body of knowledge. Although
Einstein’s theory is widely accepted, Newton’s law of universal gravitation is still used for
practical situations such as satellite motion.
superseded by Albert Einstein’s ideas that all masses distort space and time.
This highlights the fact that science is not a fixed body of knowledge. Although
Einstein’s theory is widely accepted, Newton’s law of universal gravitation is still used for
practical situations such as satellite motion.
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