An object accelerates only when the resultant force isn’t zero. However, this acceleration depends on two factors:

• The size of the force: an object accelerates in the direction of the resultant force. The larger the force is, the greater the acceleration will be. So, if you double a resultant force then the acceleration will also double.
• The mass: an object accelerates in the direction of the resultant force. A force put on a small mass will accelerate it more than the same force put on a larger mass. So, if you double the mass then the acceleration will be halved.

Acceleration can be calculated using the following equation:

a = F / m

• – F is the resultant force in newtons (N)
• – m is the mass of the object in kilograms (kg)
• – a is the acceleration of the object in metres per second squared (m/s²)

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Weight and mass

Weight and mass aren’t the same thing.

• – Mass is the amount of stuff contained within an object.
• – Weight is a force which acts on the stuff. It’s due to Earth’s gravitational field which pulls objects downwards towards the Earth’s centre.

Weight can be calculated by using the following equation:

W = m x g

• – W is the weight in newtons (N)
• – m is the mass in kilograms (kg)
• – g is the strength of the gravitational field in newtons per kilogram (N/kg)

The gravitational force on the Moon is only one-sixth of that found on Earth. This means that on the Moon you’d weigh less. However, your mass wouldn’t change.

If an object is falling to Earth then you use a different equation to figure out its weight:

W = m x a

• – W is the weight in newtons (N)
• – m is the mass in kilograms (kg)
• – a is acceleration due to gravity (m/s²)