Forces, friction, gravity
   | What is Force?Force is a push or pull acting on an object. Some examples of force are friction, gravity and applied force. Applied force is when a person or object apply force to another object. If you push someone on a swing, you are applying force to that object. Force can make an object start moving or a moving object go faster. The object can change its speed, direction or both. Force includes size and direction making it a vector. There can be more than one force acting on a object at the same time. Balanced forces are when two forces are acting on an object but the object doesn't move because they are of the same force. Unbalanced is when the object does move because one force is stronger than the other.
|
  | What is Friction? Friction is when two objects come in contact. When the two objects rub each other, they have energy and they give out heat. There are many types of friction such as: Friction opposes motion because motion does not give out force. Motion is just a change in position and friction is the opposite. Two objects come in contact in give out force. |
What is Gravity?
Gravity is defined as a force of attraction between two objects or masses. Anything that has mass, gives out gravity on other matter. Gravity is also what keeps us on the Earth and we don't fly around! Gravitys effect is that objects has a pull on other objects. Gravity can have an effect on objects that have a very large distance between them, unlike friction.
Gravity keeps the moon and satellites orbiting around us. It also keeps the Earth orbiting around the Sun. The SI unit is Newtons.
My Weight on the Planets of our Solar System
My weight on Earth is 36 kilograms. On Mercury it's 13.6 kg, on Venus it is 32.6 kg, on our moon it is 5.9 kg, on Mars it's 13.5 kg, on Jupiter it is 85.1 kg, on Saturn it's 38.3 kg, on Uranus it's 32 kg, on Neptune it is 40.5 kg and on Pluto it's 2.4 kg.
Newton's Law of Universal Gravitation
Since Isaac Newton was the first to say that gravity is universal and it happens to every object in the universe, his idea became known as the Law of Universal Gravitation. The Law of Universal Gravitation means that the force that holds us down to the Earth is the same force that makes the moon and the satellites orbit around us. It also means that the while the Earth pulls on you, you're also pulling on the Earth. Everything is attracted to each other by gravity.
Einstein's theory of Gravity
Einstein came up with a theory that predicts in a better way how all objects move. he showed mathematically that in reality gravity is not a force. He explained that gravity is the curving of time and space. As if the Sun is in a trampoline and every planet is surrounding it. The trampoline curves down. He said that Earth and every other body of mass affect space and time. He prooved that objects curve towards each other because of the curve in space and time.
How Einstein's theory differs from Newton's
While Newton could predict the motion of some but not all objects, Einstein could predict their motion in a better way. Newton thought gravity is a force but Einstein showed it actually wasn't. Whatever Newton thought, Einstein showed differently.
A boy drops an object at time t = 0 s. At time t = 1 s, the object is falling at a velocity of 9.8 m/s. What is its velocity by time t = 8?
To solve this, you have to multiply 9.8 by 8. If you multiply you'll get 78.4 m/s2
Gravity pulls you down at a speed of 9.8 m/s and after 8 seconds you would have accelerated 8 times that.
How Gravity affects the Motion of Objects
Gravity affects how fast an object falls. First it will start going horizontally, for example, then gravity pushes it down and it just falls. If you use the example of the cannon, the cannon shoots the ball into the air and it starts going horizontall but not for long. Gravity has a stronger force than the ball so it pushes it down. It curves down. That's why people shoot an arrow up when they're throwing it. By doing that the arrow will curve down and hit the target. This is called Projectile Motion.
Orbital Motion
The moon orbits around the Sun. But the Earth's gravity should pull the moon towards it but it never hits it. The moon has enough velocity to go around it. It's falling towards us but it's so far away that it falls in a circular motion around us and it never hits us. It keeps orbiting us but it never crashes.
Sources
CK- 12
fourcroy.org
ggos-portal.org
spacetourismnow.com
share.ehs.uen.org
school-for-champions.com
slimfilms.com
BRUNA VIDAL
