Weight
Gravitational force on a mass near Earth.
Formula
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Example
10 kg weighs ~98 N
How it works
This formula says that an object's weight is the downward force caused by gravity acting on its mass. Near Earth’s surface, the gravitational field strength is about 9.81 N per kilogram, so each kilogram of mass experiences about 9.81 newtons of weight. The formula works because weight is proportional to mass: doubling the mass doubles the gravitational force.
When to use it
Use this when you need the force due to gravity on an object near Earth, such as in mechanics, force diagrams, or calculating how heavy something feels. It is also useful for finding the weight of an object from its mass in newtons.
Worked example, step by step
Given: Mass, m = 7 kg Gravity, g = 9.81 m/s² Use the formula: W = mg Substitute the values: W = 7 × 9.81 Calculate: W = 68.67 N Final answer: The weight of the object is 68.67 N
Common mistakes to avoid
- Using kilograms as the final answer instead of converting to newtons
- Forgetting that g must be in m/s² or N/kg and using the wrong value
- Mixing up mass and weight, which are not the same thing
Did You Know?
Your weight would be about a sixth on the Moon, yet your mass — the actual amount of you — would not change at all.
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