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# How To Find Force Physics

## How To Find Force

Net Force Physics Problems With Frictional Force and Acceleration

Let’s look at a few exercises so that nothing can surprise you in your physics class.

1. Find the accelerating and retarding force:

A cheetah has a mass of 50 kg. It accelerates from rest to 50 km/h in 3 seconds. Then it starts steadily slowing down and stops after 8 seconds.

• Accelerating force:

50 km/h is equal to 13.89 m/s .

Acceleration is equal to difference in velocity over time:

a = / 3 s = 4.63 m/s2

Calculate accelerating force:

Fa = m * a = 50 kg * 4.63 m/s2 = 231.5 N

• Retarding force:

a = / 8 s = -1.74 m/s2

Fr = 50 kg * -1.74 m/s2 = -87 N

Retarding force is negative, because it has an opposite direction to the accelerating force.

2. How much force do you need to accelerate an object by 8 m/s2? What about when the object is three times heavier? How does it affect the force?

• F1 = 2 kg * 8 m/s2 = 16 N

• F2 = 3 * 2 kg * 8 m/s2 = 48 N

If the mass is three times heavier, the force needs to be three times bigger.

## Normal Force With An External Upward Force

• 1Use the right equation. To calculate the normal force of an object at rest when an outside force acts upward on that object, use the equation: N = m * g – F * sin’XResearch source
• N refers to the normal force, m refers to the object’s mass, g refers to the acceleration of gravity, F refers to the outside force, and x refers to the angle between the object and the direction of the outside force.
• Example: Find the normal force of a block with a mass of 4.2 kg, when a person is pulling up at the block at a 50 degree angle with a force of 20.9 N.
• 2Find the object’s weight. The weight of an object equals the mass of the object multiplied by the acceleration of gravity.
• Note that the gravitational acceleration at the Earth’s surface is a constant: g = 9.8 m/s2
• Example: weight = m * g = 4.2 * 9.8 = 41.16
• 3Find the sine of the angle. The sine of an angle is calculated by dividing the side of the triangle opposite the angle by the hypotenuse of the angle.
• Example: sin = 0.77
• 4Multiply the sine by the outside force. The outside force refers to the force acting upward on the object, in this instance.
• Example: 0.77 * 20.9 = 16.01
• 5
• ## Is Weight A Force

Weight is another term for gravitational force. In physics, weight and mass are not the same. Mass is an attribute of an object that resists any changes in motion. The weight force acting on the mass due to gravity. If its mass on the earth is 70 kilograms, then its weight is approximately 700 Newtons .

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## How To Find Net Force

This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness. wikiHow’s Content Management Team carefully monitors the work from our editorial staff to ensure that each article is backed by trusted research and meets our high quality standards.There are 7 references cited in this article, which can be found at the bottom of the page. This article has been viewed 70,451 times.Learn more…

Net force is the total amount of force acting on an object when you take into account both magnitude and direction. An object with a net force of zero is stationary. An unbalanced force, or net force of a magnitude greater than or less than zero, leads to acceleration of the object.XResearch source Once you have calculated or measured the magnitude of a force, combining them to find the net force is simple. Sketching a simple force diagram and making sure all of the forces are labelled and in the correct direction makes calculating net force a breeze.

## Impact From A Horizontally Moving Object

Now suppose you want to know the impact force of a 2,200-kilogram car traveling at 20 meters per second that crashes into a wall during a safety test. The stop distance in this example is the crumple zone of the car, or the distance by which the car shortens on impact. Suppose the car is squished enough to be three quarters of a meter shorter than it was before the impact. Again, the first step is to set the equations for energy — this time kinetic energy — and work equal to each other and solve for force.

The final step is to plug the values from the problem into the equation for force:

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## How To Find Work When Force Is Unknown

Does work done on an object depend on the force applied? EX:A 50kg barbell is lifted 1.5 meters. How much work is done?

I am confused because I do not know how much force was used to lift the barbell . I know the gravitational force but how do I calculate the net force?

My friend believes that we do not have enough information

• 1$\begingroup$For the problem you provided, don’t you just multiply the gravitational force by 1.5 meters to figure out the work? Work done against gravity is always just mgh.$\endgroup$Nov 2 ’17 at 4:17
• 1

One of the Theorems relating work and energy is $$W_ = – \Delta U,$$ where $W_$ represents the work done by the conservative forces between two points $A$ and $B$ and $\Delta U$ represents the change in the potential energy.

The work done by a force between two points $A$ and $B$ is defined as $$W_ = \int_A^B \vec \cdot \text\vec.$$

Since every force related to a potential is a conservative force, it comes easily that:

$$\vec = – \nabla U$$$$\int_A^B \vec \cdot \text\vec = – \int_A^B \nabla U \cdot \text\vec$$$$W_ = – \left$$$$\therefore W_ = – \Delta U$$

Since, when close to the ground, $U = mgh$, you just have to calculate $U – U = mg \cdot h – mg \cdot h$.

$$W = 50 \cdot g \cdot 0 – 50 \cdot g \cdot 1.5 = – 75 \cdot g$$$$\therefore W = -750 \text$$

As you can see, the work is negative, since the weight force points downwards and the displacement points upwards.

## How To Find Normal Force

wikiHow is a wiki, similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 16 people, some anonymous, worked to edit and improve it over time.There are 11 references cited in this article, which can be found at the bottom of the page. This article has been viewed 722,570 times.Learn more…

Normal force is the amount of force required to counteract the other forces in any given scenario. The best way to go about finding it depends on the circumstances of the object and the variables you have data for. Keep reading to learn more.

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## What Is Net Force

Force is a vector. It means that it has a value and direction. That’s why you can’t add it like regular numbers .

The net force is the sum of the vectors of all individual forces acting on an object. For example, let’s look at a falling ball. It is affected by the gravitational force , air resistance , and lateral force caused by wind .

• First, find the net force of horizontal forces. They have an opposite direction so, in part, they cancel each other:

• FH = FG – FR = 5N – 1 N = 4N
• Now, find the net force of the two remaining forces.

FH2 + FW2 = FN2 FN = 2â5

The Net force acting on a ball equals 2â5 N.

• Now that you know Newton’s three laws of motion, and force definition, look at one of the calculators listed at the beginning. We explain there in detail all types of forces. We also recently did a fun experiment, where we tested what would win a race – a toilet paper or a bottle?. Check it out to learn something about mass moment of inertia, and acceleration!

## How To Calculate Tension In Physics

Calculating g-force

In physics, tension is the force exerted by a rope, string, cable, or similar object on one or more objects. Anything pulled, hung, supported, or swung from a rope, string, cable, etc. is subject to the force of tension.XResearch source Like all forces, tension can accelerate objects or cause them to deform. Being able to calculate tension is an important skill not just for physics students but also for engineers and architects, who, to build safe buildings, must know whether the tension on a given rope or cable can withstand the strain caused by the weight of the object before yielding and breaking. See Step 1 to learn how to calculate tension in several physical systems.

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## What Is Normal Force

Normal force is the perpendicular force that the surface exerts on an object. For example, if you put a book on a table, there is a gravitational force that is pulling it toward the ground. To counteract this force, the table exerts a force on the book, preventing it from falling. This counteracting force is called the normal force, and is represented by FN, or N. The unit for the normal force is ‘N‘ .

The normal force is a typical example of the Newton’s third law of motion.

If one object exerts a force on a second object, the second object exerts a force of equal magnitude and opposite direction on the first object .

So, a normal force is equal to the force exerted by the object on the surface. It’s formulas vary with the slope of the surface.

• For an object lying on a flat surface, the formula is:
• FN = m * g

• m is the mass of an object.
• g is the gravitational acceleration.

According to Newton’s third law, the normal force for an object on a flat surfaces is equal to its gravitational force .

• For an object placed on an inclined surface, the normal force equation is:
• FN = m * g * cos

On an inclined surface , the weight of the object is supported by both the normal force and friction. The gravitational force of the object is not opposite and equal to the normal force, but one of the force of gravity’s vector’s components is.

To find out how to calculate normal force with friction, use the friction calculator.

## How Are Force And Motion Related

Force is any interaction that, if unopposed, can change the motion of an object. Without external force, a moving object will keep moving at a constant speed and direction, and an object at rest will stay at rest. If external, unbalanced force is applied, an object will change the motion by changing its speed and/or direction.

The relationship between force and motion is defined by Newton’s laws of motion.

## Normal Force And Friction

• 1Know the basic equation for kinetic friction. Kinetic friction, or the friction of an object in motion, is equal to the coefficient of friction multiplied by the normal force of an object. In equation format, that looks like: f = * NXResearch source
• In this equation, f stands for friction, refers to the coefficient of friction, and N refers to the normal force of the object.
• A “coefficient of friction” is the ratio between frictional resistance to normal force, which is responsible for pressing the two opposing surfaces together.
• 2Rearrange the equation to isolate the normal force. If you have a value for the kinetic friction of an object, as well as that object’s coefficient of friction, you can calculate the normal force by using the formula: N = f / XResearch source
• Both sides of the original equation were divided by , thereby isolating normal force on one side while accounting for the coefficient of friction and kinetic friction on the opposite side.
• Example: Find the normal force of a block when the coefficient of friction is 0.4 and the amount of kinetic friction itself is 40 N.
• 3Divide the kinetic friction by the coefficient of friction. This is essentially all you need to do to find the value of the normal force.
• Example: N = f / = 40 / 0.4 = 100
• 4Record your answer. If desired, you can check your answer by plugging it back into the original equation for kinetic friction. Otherwise, you have completed the problem.
• Example: The normal force is 100.0 N.
• ## Is Force A Vector

Force is a vector. That means it’s defined by both magnitude and direction. Scalars, like mass or length, are defined only by magnitude. So, if you apply two forces to an object, you can’t add them like scalars. You need to take the direction into account and find the net force – the forces’ vector sum.

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## Definition Of A Net Force

When we kick a soccer ball, then the ball takes off and moves through the air. Then, there is a net force acting on the ball. Again when the ball starts to come back to the ground and eventually stops, there is also a net force acting on the ball.

According to Newtons Second Law, when a net force is acting on an object, then that object must be accelerating. Therefore, its speed changes from second to second. Hence when we first kick the soccer ball, it accelerates, and when the soccer ball begins to slow down it is again accelerating.

Now, a net force is defined as the sum of all the forces acting on an object. The following equation is the sum of N forces acting on an object.

Where,

\ are the forces acting on a body.

When the body is at rest position then the net force formula is given by,

## Newtons Second Law In Terms Of Momentum

When Newtonâs second law is expressed in terms of momentum, it can be used for solving problems where mass varies, since Î

Î p stays the same will decrease Fnet. This is another example of an inverse relationship. Similarly, a padded dashboard increases the time over which the force of impact acts, thereby reducing the force of impact.

Cars today have many plastic components. One advantage of plastics is their lighter weight, which results in better gas mileage. Another advantage is that a car will crumple in a collision, especially in the event of a head-on collision. A longer collision time means the force on the occupants of the car will be less. Deaths during car races decreased dramatically when the rigid frames of racing cars were replaced with parts that could crumple or collapse in the event of an accident.

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## Forces In Quantum Mechanics

The notion “force” keeps its meaning in quantum mechanics, though one is now dealing with operators instead of classical variables and though the physics is now described by the SchrÃ¶dinger equation instead of Newtonian equations. This has the consequence that the results of a measurement are now sometimes “quantized”, i.e. they appear in discrete portions. This is, of course, difficult to imagine in the context of “forces”. However, the potentials V or fields, from which the forces generally can be derived, are treated similarly to classical position variables, i.e., V }} .

This becomes different only in the framework of quantum field theory, where these fields are also quantized.

Thus the notion “force” loses already part of its meaning.

The utility of Feynman diagrams is that other types of physical phenomena that are part of the general picture of fundamental interactions but are conceptually separate from forces can also be described using the same rules. For example, a Feynman diagram can describe in succinct detail how a neutron into an electron, proton, and neutrino, an interaction mediated by the same gauge boson that is responsible for the weak nuclear force.

The four fundamental forces of nature

Property/Interaction
}=m}}

, is the unit vector directed outward from the center of the Earth.

E

## Normal Force On An Incline

How to find spring force, spring constant or distance stretched (Hooke’s Law)
• 1Use the right equation. To calculate the normal force of an object at an angle, you need to use the formula: N = m * g * cosXResearch source
• For this equation, N refers to the normal force, m refers to the object’s mass, g refers to the acceleration of gravity, and x refers to the angle of incline.
• Example: Find the normal force of a block with a mass of 4.2 kg, sitting on a ramp with an incline of 45 degrees.
• 2Find the cosine of the angle. The cosign of an angle equals the sine of the complementary angle, or the adjacent side divided by the hypotenuse of the triangle formed by the incline.XResearch source
• This value is often determined by a calculator, since the cosine of any angle is constant to that angle, but you can compute it manually, as well.
• Example: cos = 0.71
• 3Find the object’s weight. The weight of an object equals the mass of the object multiplied by the acceleration of gravity.XResearch source
• Note that the gravitational acceleration at the Earth’s surface is a constant: g = 9.8 m/s2
• Example: weight = m * g = 4.2 * 9.8 = 41.16
• 4Multiply the two values together. In order to find the normal force, you need to multiply the weight of the object by the cosine of the angle of incline.
• Example: N = m * g * cos = 41.16 * 0.71 = 29.1