-FORCE & MOTION

Gravity Gravity: is a force that pulls objects downwards towards the centre of the earth or it is the attraction between you & the Earth.

Gravity affects objects on Earth all the time. It hold things to the SURFACE of the Earth. It pulls objects (big or small) towards each other. The gravity between Earth and anything on it is noticeable because the mass of Earth is so large. The pull of Earth's gravity makes any object fall to the ground. As the moon goes around Earth, its gravity pulls on Earth causing water in the oceans to move towards the moon. This movement is called tides. Earth's gravity also pulls on the moon and keeps the moon moving around Earth. In the same way, the pull of the sun keeps Earth moving around the sun.

Gravity Did you know that gravity causes falling objects to speed up as they fall? The feather and the apple are falling in vacuum( where there is no air) Photographs were taken at equal time intervals. At first the objects fell a shorter distance per interval. Later, they fell a larger distance. This shows that objects move faster, or accelerate, as they fall.

Gravity Gravity pulls the apple & the feather downwards. Their speed increase as they fall. Both fall at the same rate in a vacuum because there is no air to slow the feather. The speed of any falling object is about 10m/sec after the 1st second After another second the object falls at a speed of 20m/sec. After the 3rd second, it falls about 30m/sec ( can you see the pattern? )

All the objects in the universe pull on 1 another All the objects in the universe pull on 1 another. That they exert a “ gravitational force”. Gravitational force can be strong or weak, depending on the masses of the objects & the distance between them. Gravitational force is weaker between smaller objects and larger for objects of greater mass. The CLOSER objects are to each other, the greater the force of gravity. So The closer the objects & the greater their mass, the greater the gravitational force between them.

The moon has less mass than the Earth, so the moon pulls objects towards its center with less gravitational force. There is a simple way to measure the gravitational force acting on an object. Find the objects weight!!

Weight: is the measure of the gravitational force acting on an object. That’s why objects weigh more on Earth than they do on the moon. In other words, Earth pulls things harder ( due to more mass=more gravitational force), so they weigh more. Mass doesn’t change though, so an astronaut has the same mass on moon & on Earth.

It is measured in grams (g) or kilograms (kg) Mass & Weight Mass : the amount of matter it contains It is measured in grams (g) or kilograms (kg) but it is NOT a force. Weight : the force caused by gravity pulling down on the mass of an object. Or it is the measure of the gravitational force acting on an object.