Answer:
Explanation:
Scientific view
Gravitational forces are considered to be inherently linked to what we call ‘mass’. There is a gravitational force of attraction between every object in the universe. The size of the gravitational force is proportional to the masses of the objects and weakens as the distance between them increases. Both objects exert an equal attractive force on each other: a falling object is attracting the Earth with the same size force as the Earth is attracting it. The vast difference in mass between the Earth and the falling object means the Earth’s movement is imperceptibly small.
We only notice gravitational forces if one of the objects involved has a huge mass (such as the Earth). In all attempts to compare gravitational forces with other forces, they are relatively much weaker than magnetic and electric forces.
Critical teaching ideas
Gravitational force is an attraction between masses.
The greater the size of the masses, the greater the size of the gravitational force (also called the gravity force).
The gravitational force weakens rapidly with increasing distance between masses.
The gravitational force is extremely hard to detect unless at least one of the objects has a lot of mass.
Because the Earth is so big, you have to travel to a very great height above the Earth’s surface before there are any detectable changes in the gravitational pull of the Earth (there is only about 0.25% reduction at the top of Mt Everest).
The weight force on an object tells us the size of the gravity force from Earth acting on the object.
Explore the relationships between ideas about gravity in the Concept Development Map - (Gravity, Stars)
It is useful to focus separately on two areas where gravity is important:
1. Near the Earth’s surface
Students need opportunities for discussion that draws out the idea that gravity forces on objects are exerted by the whole Earth towards its centre. A gravity force acts on an object regardless of whether it is moving or not moving. In everyday situations, the size of the gravity force on something does not change significantly as it rises above the Earth. (An object needs to go much higher than a jumbo jet for major differences to occur. The size of the gravity force at an altitude of 200km is still about 94% of what it was at sea level.)
The gravity force on an object from the Earth is the same regardless of whether the object is surrounded by air (or water or anything else).
