Acceleration is a vector (‘Vectors are quantities which are fully described by both a magnitude and a direction.’ (Tom Henderson, 1996) quantity, which is defined as ‘the rate at which an object changes its velocity.’ (Tom Henderson, 1996) An object is accelerating if it is changing its velocity. It is calculated in this equation
A = (vf – vi) / t, where A = average acceleration
Vf = Final Velocity
Vi = Initial velocity
T = Time taken
If we slow down this is known as deceleration, as a person gets faster then they are accelerating. In order to produce acceleration, a force must be applied to the body, the bigger the force the bigger the acceleration, the bigger the mass the slower the acceleration. A 100m sprinter will keep accelerating, until he/she will reach their constant speed, this is where they are neither accelerating nor decelerating. Sports announcers will occasionally say that a person is accelerating if he/she is moving fast. Yet acceleration has nothing to do with going fast. A person can be moving very fast, and still not be accelerating. Acceleration has to do with changing how fast an object is moving. If an object is not changing its velocity, then the object is not accelerating.
A 100metre sprinter speeds up their velocity from 5 mph to 15mph, in a time period of 5 seconds; therefore we use the formula to calculate there average their acceleration. (vf – vi ) = (5 – 15) = 10 / 5 = 2 ms-2 (it is calculated in metres per second per second). The opposite of accelerating is deceleration. They are also known as positive and negative acceleration.
Although speed and velocity are similar they do have some similarities, speed represents how fast an object is going, velocity represents, the rate of change of displacement with time but has the same units as speed however. For example a marathon runner is running at 10mph this is known as speed, however if you say they are running at 10 mph in a southerly then you talking about its velocity.
Velocity is a vector quantity, which refers to ‘the rate at which an object changes its position.’ (Tom Henderson, 1996) Imagine a person moving rapidly, one step forward and one step back, then always returning to the original starting position. While this might result in a quick fire of activity, it would also result in a zero velocity. Because the person always returns to the original position, the motion would never result in a change in position. Since velocity is defined as the rate at which the position changes, this motion results in zero velocity. ‘If a person in motion wishes to maximize his/her velocity, then that person must make every effort to maximize the amount that he/she is displaced from his/her original position.’ (Author Unknown, 2004) Every step must go into moving that person further from where he/she started. The person should never change directions and begin to return to where he/she started. The following equation shows how to calculate velocity:
Velocity = displacement / time taken
For example a 200m runner, their displacement is 200metres; they took 19.80 seconds to run the 200metres. Therefore it is 200 (displacement) / 19.8 (time taken) = 10.1 is their average velocity. You need Displacement to find out what the average velocity is displacement is: is the change in position of an object in a specified direction. Displacement is a vector quantity. It does not require a reference point. This is measured in metres, it is different to distance as distance measures the length of the path the body follows, displacement measures the distance between the starting and finishing point.
Newton’s Third Law: is properly stated as ‘Forces always occur in pairs. If object A exerts a force F on object B, then object B exerts an equal and opposite force -F on object A’, but the definition that most people remember is ‘every action has an equal and opposite reaction’. In other words, when one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object. Likewise, when a skeet shooter fires his shotgun at a clay disc flying through the air, he experiences the recoil upon the shotgun. The “kick” felt by the shooter is the reaction force upon the shotgun, which is equal in magnitude to the force that pushes the pellets. For this theory first it most have two objects involved, as they cannot work together in pairs else. There exists a whole set of situations where two equal and opposite forces act on the same object, cancelling each other so that no acceleration (or even no motion) occurs.