How to Calculate Force

Reviewed by Grace Imson, MA

Last Updated: December 10, 2024 Fact Checked

Force is the "push" or "pull" exerted on an object to make it move or accelerate. Newton's second law of motion describes how force is related to mass and acceleration, and this relationship is used to calculate force. In general, the greater the mass of the object, the greater the force needed to move that object.^{[1]
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Part 1

Part 1 of 2:

Learning the Formula

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The force (F) required to move an object of mass (m) with an acceleration (a) is given by the formula F = m x a. So, force = mass multiplied by acceleration.^{[2]
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2
Convert figures to their SI values. The International System of Units (SI) unit of mass is the kilogram, and the SI unit of acceleration is m/s² (meters per second squared). So when mass and acceleration are expressed in their SI units, we get the force in its SI units which is N (Newtons).^{[3]
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- As an example, if the mass of the object is given to be 3 pounds, you'll need to convert those pounds to kilograms. 3 pounds make 1.36 kg, so the mass of the object is 1.36 kg.
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If the weight of an object is given in N (Newtons), then divide it by 9.8 to get the equivalent mass. For example, 10 N weight is equivalent to 10/9.8 = 1.02 kg.^{[4]
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Part 2

Part 2 of 2:

Using the Formula

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1
Find the force that is required to accelerate a 1,000 kg car at 5 m/s².
- Check to make sure all your values are in the correct SI unit.
- Multiply your acceleration value (1000 kg) by 5 m/s² to calculate your value.
2
Calculate the force required for an 8 pound wagon to accelerate at 7 m/s².
- First, convert all your units to SI. One pound is equal to .453 kg,^{[5]
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- Multiply your new value for the mass (3.62 kg) by your acceleration value (7 m/s²).
3
Find the magnitude of force acting upon a cart weighing 100 N and accelerating at the rate of 2.5 m/s².
- Remember, 9.80 N is equal to 1.00 kg.^{[6]
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  Research source} So, convert Newtons to kg by dividing by 9.8 kg. Your new kg value should be 10.2 kg for the mass.
- Multiply your new mass value (10.2 kg) times the acceleration (2.5 m/s²).

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How do I change Newtons into mass?

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The formula for force is force = mass * acceleration. To find mass, simply divide the force by the acceleration.

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Is force the same as weight?

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Weight is a force. When a force is due to gravity, it can be called "weight". "Weight" is only a human distinction for a specific case.

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What is the acceleration of a 130 kg object push by a man with 650 newtons of force?

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You will need to know the formula of acceleration, once you know that. You can easily get the acceleration. So by using this formula, you can figure out what acceleration. It is simply just Algebra in this case. Formula: f/m=a

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Check to be sure all numbers have been converted to kilograms and m/s^2.^{[7]
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The definition of a Newton, the standard unit of force, is N = kg * m/s^2.^{[8]
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Always read a question carefully to determine whether weight or mass is given.

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When you're answering math or physics questions, make sure that you read the prompt and equation carefully. I've seen so many people get tripped up just because they misunderstood the question.
Make sure you don't mix up weight and mass. The two variables seem like they'd be the same thing but they aren't.

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