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# Overview of Motion

by Ron Kurtus (revised 28 April 2018)

An object is in motion when it is continuously changing its position relative to a reference point, as observed by a person or detection device. In other words, motion is a study of relative position, speed, and acceleration.

Isaac Newton stated three laws of motion that explain its functions and restraints. These laws affect the different types of motion.

Some questions you may have include:

• Why is motion relative?
• What are Newtons laws?
• What are the different types of motion?

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

## Motion is relative

All motion is relative to the observer or to some fixed object that is your point of reference.

### Speed and velocity

Speed is how fast an object is going with respect to a point of reference. It is measured as distance traveled divided by time. The distance could be a straight line or along a curved path.

Velocity is a measure of the speed in a given direction. You can say the top speed of an airplane is 300 kilometers per hour (kph). But its velocity is 300 kph in a northeast direction. The equation for velocity is:

v = d/t

where

• v is the velocity
• d is the displacement or distance in a straight line
• t is the time interval

### Acceleration

Acceleration is the increase of velocity over a period of time. Deceleration is the decrease of velocity. When you start running, you accelerate (increase your velocity) until you reach a constant speed.

Mathematically, acceleration is the change in velocity divided by the time for the change

## Laws of motion

Isaac Newton defined three laws concerning the behavior of moving objects way back in 1687. These scientific statements help to explain the nature of matter and motion.

Newton's first law of motion is often called the Law of Inertia. It states that an object in motion remains in linear or rotational motion until acted upon by some force.

His second law shows the relationship between force and acceleration, while his third law is often called the Action-Reaction Law of Motion and can relate to collisions.

## Types of motion

The major types of motion are linear, rotational, and periodic.

### Linear

Linear motion means the object moves in a straight line. Newton's Law of Inertia dictates linear motion unless affected by a force changing the direction of the object.

#### Collision

A collision is a special type of linear motion where momentum and energy—and thus motion—may be transferred when two objects collide or smash into each other.

### Rotational

An object can rotate about its center of mass. The Law of Inertia applies in a special case, such that the object will continue to rotate unless constrained or affected by a force.

### Periodic

An object or group of objects can be made to move back-and-forth in periodic motion if the motion is constrained and some continues force is applied. The example of a pendulum show periodic motion. Its motion is constrained by the string, while the force of gravity keeps it in motion.

## Summary

Motion is change in position. All motion is relative to some fixed point or object. Speed is a measurement of that change in position over time. Velocity is speed in a given direction. Acceleration is the increase in speed or velocity over a period of time.

Isaac Newton stated three laws of motion that explain its functions and restraints. These laws affect the different types of motion.

Move; Do something; Excel

## Resources and references

Ron Kurtus' Credentials

### Websites

Kinematics - Wikipedia

1-D Kinematics - The Physics Classroom

Physics Resources

### Books

Top-rated books on the Physics of Motion Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.

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