# Motion, Speed, Velocity and Acceleration

### Motion:

Motion happens to be one of the interesting topics in physics and is said to occur when something moves. We live in a universe where everything moves, although at a different rate. For instance:

• The earth orbits or revolves round the sun
• The moon revolves round the earth (as earth’s satellite)

In physics, motion refers to a change in the position of an object with reference to time.

Although we may sometimes sit or stand in a fixed position, that doesn’t mean motion isn’t taking place. The fact that the earth is rotating implies that we are indirectly moving along with it.

We can thus say that motion can be relative to some frame of reference.

In the above instance, the earth (constantly rotating along its axis) is our frame of reference and everything present on earth is in motion with regard to earth as a frame of reference.

Another instance can be attributed to someone sitting inside a moving bus. The person will appear to be static (not moving). Based on the fact that the bus is in motion (moving), we can conclude that the motion of the person sitting inside the bus is relative to the bus.

Force is responsible for the motion/movements present in the universe. For an object to move, a force must act upon it. For instance, if we keep a pin in a vacuum and it’s left untouched, the pin will remain in that position "forever" unless it is acted upon by a force. This force could be in the form of an applied air or a deliberate touch by humans.

In order to get a better understanding of motion, it is important we know how the following terms work since they all involved in motion. The terms are:

### 1. Speed

Speed is simply the rate of motion since it is a measure of how fast or slow an object is moving. The dimensions associated with speed are distance and time. For instance, if one covers a distance of 10000 meters in 50 seconds and another covers the same distance in 5000 seconds, we can conclude that the first person has a faster speed than the second person because he covered the same distance at a lesser time.

Speed is defined as distance travelled per unit of time OR the rate of change of distance

Speed = distance/Time

Note: Distance is the total length of path traveled from one point to another. It is measured in meters.

Time is a duration or period during which things happen. It is measured in seconds.

Speed is a scalar quantity since it is has only magnitude and no direction

### 2. Velocity

Although velocity and speed are often used interchangeably by students, they are NOT the same thing. The direction in which an object is moving is what differentiates velocity from speed.

Velocity can be defined as speed in a given direction OR the rate of change of displacement.

It is a vector quantity because it has magnitude and direction

Velocity = Change in distance/Change in time

The statement below differentiates speed from velocity.

A bus is moving on a highway at a speed of 100 meters per 20 seconds. When the bus changes its direction and moves at a different speed (or even the same speed), that’s velocity. For instance, the bus may move at a velocity of 100m/20s in the northern direction and 200m/20s in the eastern direction.

Note: Speed and velocity both have the same Standard International unit which is meter per second (m/s)

### 3. Acceleration

The velocity of a moving object can either decrease or increase over a period of time; and this is where acceleration comes into play. For instance when you ride a bicycle, you start slowly but as soon as you increase the push on the pedals, the bicycle moves faster (accelerate). When you stop pushing the pedals, the bicycle begins to move slowly (negative acceleration).

From the above, we can therefore say that acceleration can also be negative.

Note: Deceleration is an English term used to describe negative acceleration; but in physics, we use the term acceleration to denote both the positive and negative changes in velocity.

Acceleration can be defined as the rate of change of velocity
OR
The measurement of how much the velocity of an object changes with time.

Acceleration = Change in velocity/Change in time

If an object changes velocity after a fixed amount of time, then such acceleration is called constant acceleration. Take for instance, if we throw a table tennis ball down a slope, it will roll downwards more rapidly at each second. On the 1st second its velocity could be 20m/s; on the 2nd second, its velocity becomes 25m/s and on the 3rd second, it becomes 30m/s and so on. Such ball is said to have a constant acceleration of 5m/s. (That is, for every 5 meters moved, the tennis ball accelerates by one second).

Average acceleration is the total change in velocity over a period of time, divided by the duration of that period.

Note: Acceleration is a vector quantity and its Standard International unit (SI unit) is meter per second (m/s) or meter per second square (m/s2) Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.

#### NOTABLE POINTS IN Physics Fuses are present in many electrical devices. They are basically 🔥 fire-breakers 🔥 If there is a power surge, the fuse will break, preventing damage to the electrical devices. It will also prevent the incidence of 🔥 fire🔥 on/from such device. Physics is one of the core sciences. Physics is defined the scientific study of matter and the movement of matter through the space and time of the universe. Understanding the basic and fundamental concepts of physics will help you better comprehend this subject. Below are some of the concepts: The Laws of Motion (Classical Mechanics) Electromagnetism Relativity Thermodynamics Please read on the basic introduction of the above physics concept here

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