Acceleration is a word that is used frequently in everyday conversation. People use it to describe how something is changing, whether that is change in direction, change in speed, or change in magnitude.
Acceleration is a dimension of movement just like distance and time. When someone says that something is accelerating, they are saying that the object is changing its acceleration magnitude or direction.
Acceleration can be described as the rate at which the velocity of a moving object changes. Velocity is the speed and direction of a moving object. When the acceleration of an object changes, this means that the speed or direction of the object changes at a higher rate than before.
Acceleration can be negative, zero, or positive. Negative acceleration means that the velocity of an object is decreasing at a higher rate than before. Zero acceleration means that the velocity of an object remains the same. Positive acceleration means that the velocity of an object increases at a higher rate than before.
Definition of direction
The word direction often refers to the concept of direction as defined in physics. This is due to the fact that, in most cases, the word direction is used in everyday language.
In physics, the concept of direction refers to whether or not an object is moving in a positive or negative region of space-time.
To explain this concept more clearly, let us use the basics of physics: velocity and acceleration. Velocity refers to the rate at which a moving object changes its position, which is measured in meters per second (m/s).
Acceleration, on the other hand, refers to the change in velocity over a certain period of time. Acceleration can be either positive or negative, meaning that an object’s velocity can either increase or decrease.
When someone says that “the direction” they are going in is “up”, they are most likely referring to going up in altitude (going up = positive direction).
Definition of speed
Speed is the distance traveled per unit of time. Speed can be described as how fast an object moves, how far it moves, or how rapidly it changes position or direction.
Speed is a vector quantity, which means it has a direction as well as a magnitude. A car that travels east at 10 miles per hour has a speed of 10 miles per hour, but its direction is east.
Speed can be expressed in meters per second (m/s), kilometers per hour (km/h), feet per second (ft/s), or miles per hour (mph). One kilometer per hour is equal to one thousand meters per second. One mile per hour is equal to one thousand feet per second. One mph is equal to one thousand miles per day.
Acceleration can be defined as a change in velocity, which is speed in a given direction. When acceleration is not constant, it means that the velocity of the object changing speed changes over time.
Example of car moving forward at constant speed
Let’s say you are standing on a track, watching a runner. You can see that the runner’s feet are moving forward, so you know that the runner is moving forward.
You can also see the sweat on the runner’s face, so you know that he or she is working hard. By looking at his or her face, you can tell that he or she is trying to move forward faster.
You can also see the other runners in front of him or her, and notice that he or she is trying to catch up to them. You can tell that he or she is accelerating, not just moving forward at a constant speed.
Acceleration means changing your velocity, or speed and direction, in the positive direction. When someone accelerates in the positive direction, they are speeding up.
Example of car slowing down
Imagine a car that is speeding up along a highway. Then, the car suddenly shifts into reverse and starts moving backwards.
What happened? The car did not lose its forward momentum. It was still speeding up in the positive direction, towards the destination.
Instead, someone inside the car switched directions. They shifted into reverse instead of continuing to accelerate forward.
This is an important distinction to make when thinking about acceleration. A changing direction of motion is not the same as no change in speed!
Acceleration only happens in the positive direction, so when a moving object changes direction, it is no longer accelerating. It may seem weird at first, but it is important to understand this concept.
Example of car speeding up
A car that is already moving can speed up in two ways. The driver can put the car in gear and press down on the gas pedal, adding fuel to the car and accelerating the vehicle.
Another way a car that is moving can accelerate is if something pulls it forward, making it go faster. For example, a strong wind could push a stopped car forward, making it accelerate.
In both of these cases, we can say that the acceleration of the car is not due to a change in direction. The wind does not push the car either forward or to one side or the other. It only pushes it forward, straight ahead.
Acceleration can be described as a change in velocity with time. Velocity refers to how fast something is moving, and time describes how long it takes for this change in velocity to occur.
Forces affecting acceleration
When we talk about acceleration, we’re really talking about changes in velocity — how quickly an object changes its position or direction.
Acceleration is the result of a change in force, or a change in motion. When you press on a object, it accelerates in the direction you push.
That push is a force that affects its acceleration. There are two kinds of forces that can do this: Force of attraction, like gravity; and force of opposition, like friction.
When you jump off a diving board, you feel gravity pulling you down at a certain speed. You have to exert effort to avoid accelerating downward because of that force of attraction.
If there was no gravity and you jumped off the board, you would not have to work as hard to avoid accelerating in any direction — up or down — because there would be no force affecting your acceleration.
Linear acceleration vs rotational acceleration
Linear acceleration, or changing the speed of a moving object in a straight line, is different than rotational acceleration, or changing the speed of a moving object’s rotation.
Linear acceleration always means that a moving object is speeding up. If you are on a train that is accelerating and you are standing still, you will be pushed back into the wall of the train due to the increased speed of the train.
If you are on a train that is decelerating and you are standing still, you will be pushed forward into the floor of the train due to the decreased speed of the train.
Rotational acceleration does not always mean that a moving object is speeding up or slowing down. If you are on a spinning merry-go-round and stand still, you will not be pushed in any direction due to rotational acceleration.
Newton’s laws of motion
In addition to the law of action and reaction, Newton also formulated three laws of motion. The first law states that a body remains at rest or in motion unless acted upon by an outside force.
The second law states that the rate of change of velocity is proportional to the force acting on the object and opposite its direction. In other words, if you push something harder, it will change velocity (speed or direction) faster.
The third law states that for every action, there is an equal and opposite reaction. When you push against something, it pushes back on you with an equal amount of force. This applies to situations like wrestling, where you try to throw someone down but they pull you down with them.
These laws are general truths about how objects move, but they can’t always be applied to every situation. Sometimes there is no outside force acting on a object and yet it moves; this happens due to other internal forces within the object.
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