Force is a physics term that is defined as an influence that causes an object to change its rate or direction of movement or rotation. A force can accelerate objects by pulling or pushing them. The relationship between force, mass, and acceleration was defined by Isaac Newton in his second law of motion, which states that an object's force is the product of its mass and acceleration. If you want to know how to measure force, just follow these steps.
Method 1 of 2: Measure Force
1Understand the relationship between force, mass, and acceleration. The force of an object is simply the product of its mass and acceleration. This relationship can be defined by the following formula: Force = Mass x Acceleration. Here are a few other things to keep in mind as you measure force:
- The standard unit for mass is kilograms (kg).
- The standard unit for acceleration is m/s2.
- The standard unit for force is the newton (N). The newton is a derived standard unit. 1N = 1 kg x 1m/s2.
2Measure the mass of a given object. An object's mass is the amount of matter that it contains. The mass of an object never changes, no matter what planet it's on; while weight fluctuates depending on gravitational pull, your mass is the same on Earth and on the Moon.In the metric system, mass can be expressed in grams or kilograms. Let's say the object we're working with is a truck that has a mass of 1000 kg.
- To find the mass of a given object, place it on a triple beam or a double pan balance. This will calculate the mass in kilograms or grams.
- In the English system, mass can be expressed in pounds. Because force can also be expressed in pounds, the term "pound-mass" has been coined to distinguish its usage. However, if you find the mass of an object using pounds in the English system, it's best to convert it to the metric system. If you know an object's mass in pounds, simply multiply it by .45 to find the mass in kilograms.
3Measure the object's acceleration. In physics, acceleration is defined as a change in velocity, which is defined as speed in a given direction, per unit of time. In addition to the common definition of acceleration as speeding up, it also can mean an object is slowing down or changing direction. Just as velocity can be measured with a speedometer, acceleration is measured with an accelerometer. Let's say the acceleration of the 1000 kg truck we're working with is 3m/s2.
- In the metric system, velocity is expressed in centimeters per second or meters per second, and acceleration is expressed as centimeters per second per second (centimeters per second squared) or meters per second per second (meters per second squared).
- In the English system, one way to express velocity is as feet per second, so acceleration can be expressed in feet per second squared.
4Multiply the object's mass by its acceleration. This is the force's value. Simply plug in the known numbers into the equation and you will know the force of the object. Remember to state your answer in newtons (Ns).
- Force = Mass x Acceleration
- Force = 1000 kg x 3m/s2
- Force = 3000N
Method 2 of 2: Advanced Concepts
1Find mass if you know force and acceleration. If you know the force and acceleration of an object, simply plug them into the same formula to find the object's mass. Here's how to do it:
- Force = Mass x Acceleration
- 3N = Mass x 3m/s2
- Mass = 3N/3m/s2
- Mass = 1 kg
2Find acceleration if you know force and mass. If you know the force and mass of an object, simply plug them into the same formula to find the object's mass. Here's how to do it:
- Force = Mass x Acceleration
- 10N = 2 kg x Acceleration
- Acceleration = 10N/2kg
- Acceleration = 5m/s2
3Find the acceleration of an object. If you want to find the force of an object, you can calculate its acceleration as long as you know its mass. All you have to do is use the formula for finding the acceleration of an object.The formula is (Acceleration = Final Velocity - Initial Velocity)/Time.
- Example: A runner reaches a speed of 6 m/s in 10 seconds. What is his acceleration?
- The final velocity is 6 m/s. The original velocity is 0 m/s. The time is 10s.
- Acceleration = (6 m/s - 0 m/s)/10s = 6/10s = .6m/s2
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- Mass can also be expressed in slugs, with a slug equal to 32.174 pounds-mass. A slug is the amount of mass that 1 pound-force can accelerate at 1 foot per second squared. When multiplying a mass in slugs by acceleration in feet per second squared, the conversion constant isn't used.
- Thus, a mass of 640 pounds-mass accelerating at 5 feet per second squared carries an approximate force of 640 times 5 divided by 32 or 100 pounds-force.
- Weight is the expression of a mass being acted on by the acceleration due to gravity. At Earth's surface, this acceleration is about 9.8 meters per second squared (9.80665), or 32 feet per second squared (32.174). Thus, in the metric system, a 100 kilogram mass weighs about 980 newtons, and a 100 gram mass weighs about 980 dynes. In the English system, mass and weight can be expressed in the same units, so 100 pounds of mass (or pounds-mass) weighs 100 pounds (pounds-force). Because a spring scale measures the pull of gravity on an object, it actually measures weight, not mass. (In common usage, there is no distinction, so long as the only gravity under consideration is that of Earth's surface.)
- Divide the result by a conversion constant if you're working with English units. As noted above, "pound" can be either a unit of mass or force in the English system; when used as a unit of force, it is called "pound-force." The conversion constant is 32.174 pound-feet per pound force second-squared; 32.174 is the value of acceleration due to Earth's gravity in feet per second squared. (To simplify the math here, we'll round to a value of 32.)
- Note that the relationship between force, mass and acceleration means that an object with low mass and high acceleration can have the same force as an object with high mass and low acceleration.
- A mass of 150 kilograms accelerating at 10 meters per second squared carries a force of 150 times 10, or 1500 kilogram-centimeters per second squared. (A kilogram meter per second squared is called a newton.)
- Forces may have special names depending on how they act on an object. A force that causes an object to speed up is called thrust, while a force that causes an object to slow down is called drag. A force that changes the way a rotating object spins around its axis is called torque.
- A mass of 20 grams accelerating at 5 centimeters (2.0 in) per second squared carries a force of 20 times 5, or 100, gram-centimeters per second squared. (A gram centimeter per second squared is called a dyne.)
Things You'll Need
- Balance or spring scale
- Pencil and paper or calculator
Sources and Citations
- ↑ http://library.thinkquest.org/10796/ch4/ch4.htm
- ↑ http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/2-what-is-mass.html
- ↑ http://www2.franciscan.edu/academic/mathsci/mathscienceintegation/MathScienceIntegation-856.htm#item857
- ↑ http://www2.franciscan.edu/academic/mathsci/mathscienceintegation/MathScienceIntegation-836.htm
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Español: Cómo medir la fuerza, Italiano: Come Misurare la Forza, Deutsch: Die Kraft eines Objekts bestimmen, Português: Como Medir a Intensidade de uma Força, 中文: 测量力, Русский: рассчитать силу, Français: Comment mesurer une force, Bahasa Indonesia: Mengukur Gaya
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