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# Applied Force

by Ron Kurtus

Usually, when you think of a force, you are considering an applied force, which is an interaction of one object on another that causes the second object to accelerate, change velocity, or change direction.

The force can be a push, pull, or drag. The resulting direction of an object depends on the relative direction of the force on the object.

A force equation shows the relationship between force, mass, and acceleration. The object will accelerate as long as the force is being applied.

Questions you may have include:

• What are types of applied forces?
• What is the result of the direction of the force?
• What is the force equation?

This lesson will answer those questions. Useful tool: Units Conversion

## Types of applied forces

A force can be applied to another object by a direct push, pull, or drag. A collision is a form of a pushing application. A force at a distance is a form of pulling force.

### Push

The most common form of force is a push through physical contact. Simple examples include:

• You can push on a door to open it
• You can lift an object off the floor
• You can throw a ball
• The wind can push you
• A machine can push something

A pushing force is usually the result of some complex process, such as a chemical reaction.

#### Collision

When one object collides with another object, the velocity of both objects will change. In a perfectly elastic collision. the change in velocity is instantaneous. Although a "force" is applied, there is no acceleration. It is mainly a transfer of momentum and energy.

Most collisions are inelastic, meaning that some energy is lost and there is a time lag between the transfer of momentum. In such a case, the force is called an impulse force. Since there is a time lag, the force equation can hold.

### Pull

You can apply a force by directly pulling on an object, such as pulling on a rope to move a box. A special form of pulling is a force at a distance.

#### Force at a distance

Gravitation, magnetism, and static electricity are some of the forces that act at a distance with no physical contact required to move objects. They typically pull on the object.

Whereas many forces are created, these forces occur in nature.

### Dragging

If two objects or materials are in contact, and both are allowed to move, the motion of one object can cause motion on the other due to the friction between the surfaces. This dragging effect is different from the resistive force of friction, where one fixed object or material passively restricts the motion of another object.

## Results of the direction of the force

The results of the direction that the force is applied on an object vary with the motion of the object.

### Stationary object

A force applied on a stationary object will move that object in the direction of the force unless there is a large enough resistive force holding it back.

### Moving object

A force applied on a moving object in the same direction of motion will accelerate or increase the speed of that object. This can be seen when pushing on a rolling wagon.

A force applied on a moving object in the opposite direction of motion will reduce the speed of that object. For example, you might slow down when walking into a brisk wind.

### At an angle

A force applied at an angle to the motion of an object can not only change its speed but also change its direction. This can be seen by the curved path of the planets due to the gravitational pull from the Sun.

## Force equation

The acceleration caused by an applied force is:

a = F/m

This relationship is more often written as the force equation:

F = ma

where:

• F is the force required to overcome the inertia of an object
• m is the mass of the object
• a is the acceleration caused by the force

Note that the object will accelerate as long as the force is being applied. Once the force stops, the object will move freely at a constant speed unless held back by a resistive force.

## Summary

An applied force is an interaction of one object on another that causes the second object to accelerate or change velocity or direction.

The force can be a push, pull, or drag. The resulting direction of an object depends on the relative direction of the force on the object.

A force equation is F = ma. The object will accelerate as long as the force is being applied.

Be a force in your community

## Resources and references

Ron Kurtus' Credentials

### Websites

Types of Forces - Physics Classroom

Forces - Physics Hyperbook

Force - Wikipedia

Finding Acceleration - Physics Classroom

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Top-rated books on Physics of Force ## Students and researchers

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