Gravity What is it? es/cych/apollo%2010 /story/hoi/ball3.html es/cych/apollo 10/story/hoi/ball.html

Gravity is … A natural force that pulls all objects toward the center of the earth. A natural force that pulls all objects toward the center of the earth.

WHAT IS A FORCE? A pull or a push on an object It is measured in Newtons (N) or kg/ m/ s 2.

Newton was a Smart Guy Sir Isaac Newton ( ) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion Sir Isaac Newton ( ) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.

1 st law: An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force. -Things will keep moving forever unless it is stopped by a force. -Things will stay stationary (in one place) unless an outside force acts on it. If a golf ball was hit in space would it stop? If a golf ball was hit on Earth, would it to stop? What causes is to stop? - Earth’s Gravity causes things to stop. The opposing force that slows things down is Friction

Some Examples from Real Life Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion. A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

Newton’s First Law is also called the Law of Inertia -Inertia: the tendency of an object to resist changes in its state of motion -All objects have inertia. -The more mass an object has, the more inertia it has (and the harder it is to change its motion).

More Examples from Real Life A powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them. On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).

2 nd law: Force equals mass times acceleration. Gravity is a force. Gravity is a force. Acceleration is how quickly an object is changing speed Acceleration is how quickly an object is changing speed Earth’s gravity has a constant acceleration downward. All objects accelerate at 10 m/s 2. (9.8 m/s 2) Earth’s gravity has a constant acceleration downward. All objects accelerate at 10 m/s 2. (9.8 m/s 2) If we all jumped out of a plane we would fall at 10 m/s 2. This goes for all other objects whether large or small.

Which do you think would fall first? A bouncy ball A bouncy ball Or a marble

-All things fall at the same rate of speed, because of Earth’s constant downward acceleration. - But things with more mass (weight) will fall harder and hits the earth with more force! ( Gravity has a stronger force on things with more mass!)

It takes force to overcome gravity! Throw a bean bag in the air and then… Throw a basketball in the air. Which one was harder to throw? The basketball would be harder to throw. You had to use more force to throw the basketball because it has more mass (weight)

What does F = ma say? F = ma basically means that the force of an object comes from its mass and its acceleration. -Something very small that’s changing speed very quickly, like a bullet, can still have a great force. -Something very small changing speed very slowly will have a very weak force. -Something very massive that’s changing speed very slowly like a glacier, can still have great force.

Using Force = mass x acceleration Calculate which would land with more force: Calculate which would land with more force: Object 1 has a mass of 20 grams =.02 kg Object 1 has a mass of 20 grams =.02 kg Object 2 has a mass of 100 grams =.1 kg Object 2 has a mass of 100 grams =.1 kg Acceleration is 10 m/s 2. Acceleration is 10 m/s 2. Force of Object 1? Force of Object 1? Force of Object 2? Force of Object 2?

3 rd Law: For every action there is an equal and opposite reaction. ~ For every force acting on an object, there is an equal force acting in the opposite direction. -Right now, gravity is pulling you down in your seat, but your seat is pushing up against you with equal force. This is why you are not moving. -There is a balanced force acting on you– gravity pulling down, your seat pushing up.

Think about it... What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).

Satellites are objects that move fast enough that they overcome earth’s gravitational pull, but still stay within the earth’s orbit. (As you know Satelittes move around our earth. But did you know that is a problem?)

“There are currently over eight thousand satellites and other large objects in orbit around the Earth, and there are countless smaller pieces of debris generated by spacecraft explosions and by collisions between satellites. Until recently, it has been standard practice to put a satellite into orbit and leave it there. However, the number of satellites has grown quickly, and as a result, the amount of orbital debris is growing rapidly. Because this debris is travelling at orbital speeds (7-8 km/s!), it poses a significant threat to the space shuttle, the International Space Station, and the many satellites in Earth orbit.” “There are currently over eight thousand satellites and other large objects in orbit around the Earth, and there are countless smaller pieces of debris generated by spacecraft explosions and by collisions between satellites. Until recently, it has been standard practice to put a satellite into orbit and leave it there. However, the number of satellites has grown quickly, and as a result, the amount of orbital debris is growing rapidly. Because this debris is travelling at orbital speeds (7-8 km/s!), it poses a significant threat to the space shuttle, the International Space Station, and the many satellites in Earth orbit.” ebImages/OrbitalDebris.jpg&imgrefurl= alDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=250&w=2 58&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&tbnh=109&tb nw=112&prev=/images%3Fq%3Dearth%2B%252B%2Bsatellites%26 gbv%3D2%26hl%3Den%26safe%3Dactive ebImages/OrbitalDebris.jpg&imgrefurl= alDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=250&w=2 58&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&tbnh=109&tb nw=112&prev=/images%3Fq%3Dearth%2B%252B%2Bsatellites%26 gbv%3D2%26hl%3Den%26safe%3Dactive

When do Satellites become subject to earth’s gravity? -Objects must move very quickly to orbit the earth. - If an object does not meet the required speed it would be slowly dragged into the Earth’s atmosphere. -Objects farther from earth experience less gravitational pull. -The closer to earth’s surface the more gravitational pull is felt.

-The Moon orbits the Earth and is therefore a Satellite. Despite that the moon is much farther it is still attracted to the Earth’s gravitational pull, Despite that the moon is much farther it is still attracted to the Earth’s gravitational pull, -but it moves so quickly it revolves the planet at a fixed distance. -but it moves so quickly it revolves the planet at a fixed distance.

-The Moon is also 1/6.25 the size of the earth and therefore has 1/6.25 of the gravitational pull. -Earth’s gravity is 9.8 m/s 2. -Moon’s gravity is m/s2.