Mass, weight and gravity
- The mass of an object is how much matter the object is composed of. It is measured in Kilograms.
- The weight of an object is the force of gravity multiplied by the mass of the object. It is measured in Newtons.
- The mass of an object remains the same everywhere, whereas the weight of an object depends on the gravitational force exerted by the planet.
- Altogether, there is an equation that summarises the relationship between mass, weight and acceleration:
W = mg Or Weight = mass x acceleration due to gravity.
- The gravitational pull exerted by the earth is 10m/s2
- The earth’s gravitational field is equal at all points; if a hiker climbs a mountain, his weight will be he same when at ground level. This is known as a uniform gravitational field.
- This causes all objects to fall over the earth’s surface with the same acceleration.
- Air resistance is a force which can alter the acceleration of an object; see the example below:
Parachutists make use of air resistance:
- When a parachutist falls from the air, the force exerted by his weight is greater than the force exerted by air resistance.
- However, as he falls, his air resistance and the force exerted by his weight become equal; the parachutist stops accelerating and falls at a steady rate. This is known as terminal velocity.
- At this point, the parachutist opens his parachute. This greatly increases his air resistance and he begins to slow down. He needs to reach another point of terminal velocity where he can surface safely.
- Mass and weight are different.
- Mass is a measure of the amount of matter in an object when it’s not moving.
- Weight is a gravitational force on an object that has mass.
- Basically, weight is the effect of a gravitational field on a mass.
- The strength of gravitational field can be described as force per unit mass.
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