Preliminary terms
Possibly everyone has heard of the apple which fell on Isaac Newton's head. If It did, it set him asking himself why.
The grasp of gravity gives weight to its grasp on objects. Your weight is the force you exert on the Earth. The grasp of gravity stops you flying off into space.
A spacecraft leaving the surface of Earth, ... needs to be going about 11 kilometers (7 miles) per second, or over 40,000 kilometers per hour (25,000 miles per an hour), to enter orbit. source
If nothing else, this website and the talk aim to improve the prospect of members having more than an "apples fall off trees" grasp of gravity.
1 Gravity - Newton
- Sir Isaac Newton was an English mathematician .. and physicist who lived from 1642-1727.
- The legend is that Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature.
- Whatever really happened, Newton realized that some force must be acting on falling objects like apples because otherwise they would not start moving from rest.
- Newton also realized that the moon would fly off away from Earth in a straight line tangent to its orbit if some force was not causing it to fall toward the Earth.
- The moon is only a projectile circling around the Earth under the attraction of Gravity.
- Newton called this force "gravity" and determined that gravitational forces exist between all objects.
2 - Gravity - weakest force
- Gravity is a force of attraction that exists between any two objects.
- There is a force of gravity between the sun and the Earth, between the Earth and us, and even between two marbles.
- Projectiles, satellites, planets, galaxies, and clusters of galaxies are all influenced by Gravity.
- Gravity is the weakest of the four known forces of nature , yet the most dominant force.
- Even though it's the weakest force, Gravity holds together entire solar systems and galaxies!
- The force of attraction between you and the Earth is your weight.
source of 1 and 2
3 - Light There's a lot here. If in a hurry keep to the green text.
- Light travels as waves .... like the ripples in a tank of water. The direction of vibration in the waves is at 90° to the direction that the light travels.
- Unlike sound waves, light waves can travel through a vacuum (empty space). They do not need a substance to travel through, ...
- Light travels extremely quickly. Its maximum speed is approximately 300,000,000 metres/second, when it travels through a vacuum. 186,282 miles per second source
- The very large difference between the speed of light in air (almost 300,000,000 metres per second) and the speed of sound in air (343 m/s) explains why you:
- see lightning before you hear it - see a firework explode before you hear it - see a distant door slam before you hear it - source