iii-Weight
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Mass & Weight
Weight = force of gravity = mass x free fall acceleration = ma = mg
Force = Weight = mg
the acceleration of free fall for a body near to the Earth is constant
Notes:-
10 m/s2 = 10 N/kg
- Weight is the force which causes an object to accelerate downwards and has the value mg.
- The value of the acceleration caused by weight can be calculated from Newton’s second law, using the equation F = ma
- Weight unit is N (because it is a force)
- It is measured by spring balance
| Mass | Weight | |
| Define | It is the amount that body contains“It is not a force” | It is the force of gravity acting on the body“It is a force” |
| Units | kg | N (kg.m/s2) |
| Scalar or vector | Scalar quantity(No direction) | Vector quantity(always vertical downwards) |
| Device used to measure | Pan balance.Beam balance. | Spring balance |
| Dependence on place | Mass of a body remains the same throughout the universe (doesn’t change from one place to another) |
Weight varies from one place to another depends on the value of (g) which is the acceleration due to gravity. |
| The relationship between them | Weight = mg | |
Notes:-
- The weight of any object on the moon is 1/6 its weight on the earth, so gmoon = 1.67 m/s2.
- If the weight of 1kg mass will be 10 N, and since the weight = 10 x mass, so if you measure your weight on a scale (on earth) and your weight was 600 N, we can write it on the scale as 60 kg.
- The acceleration due to gravity is constant at the same place and height, can be taken as …… 10 m/s2.
- Free fall acceleration = g = weight / mass = constant (10 m/s2).
Gravitational force
Hany El-Gezawy
IGCSE Physics 