# Let’s Get Physics-l: Definitions in Kinematics

(Please Note: The Characters used in my examples are property of Marvel Comics and I, in no way, created them. They are simply being used to demonstrate a theory. Thank you)

Kinematics is the study of motion of objects and their spatial relationships, where the mass of the object and the forces causing motion are ignored. There are a couple of key words that apply to kinematics which are key when considering anything related to it.

The displacement of an object is the distance between the object and its origin (start point). Displacement is a vector quantity (A quantity with magnitude and direction) as it is a distance away from an object. It is measured in m or km. To give it some context, if Hydra are causing havoc in downtown Manhattan, Captain America and Falcon must travel 20km south, displacing them 20km south of the Avengers tower, to apprehend the thugs.

The distance of an object is the how far an object has travelled in total, regardless of whether or not they double back towards their start point. Distance is a scalar quantity (A quantity that has only magnitude) and it is measured in km or m. After defeating the Hydra thugs, Cap and Falcon return to Avengers Tower. During this time, they have travelled a total of 40km, 20km to the battle zone and 20km back to the Tower. Upon returning to the tower their displacement would be 0km as they are back at their start point.

The speed of an object is how fast it can travel over a distance in a given time. As we are not given a direction for speed, speed is a scalar quantity and it is measured in ms^-1 or kmh^-1. When considering speed, there are two types: average which is total distance travelled divided by the time taken to complete the journey and Instantaneous which is the speed at an actual point in time. Whilst Cap and Falcon are fighting Hydra south of Avengers Tower, A.I.M have seized the opportunity to attack another part of Manhattan north of Avengers tower. Quicksilver is on hand to apprehend aim and travels at a speed of 500 ms^-1 to get to the other battle zone. At 10 seconds he is travelling at 500 ms^-1 but at 20 it had increased to 600 ms^-1. His average speed come out at 550 ms^-1.

The velocity of an object is how fast it can travel in a given direction. This given direction makes velocity a vector quantity and it is measured in kmh^-1 or ms^-1. Before setting off on his journey, Quicksilver quickly takes down the general direction of where A.I.M are causing trouble (Being a speedster grants him the luxury of not having to take exact bearings). He travels in the direction of North East at a speed of 500ms^-1.

The acceleration of an object is rate of change of velocity experienced by an object. As it is the rate of change of velocity, it is a vector quantity and it is measured in ms^-2. During his journey, as mentioned above, Quicksilver increases his speed from 500ms^-1 to 600ms^-1. He accelerated at a rate of 10 ms^-2 which you can calculate using:

# a = (v-u)/t

• a – acceleration (ms^-2)
• v – final velocity (ms^-1)
• u – initial velocity (ms^-1)
• t – time taken (s)

Summary

• Displacement – Distance away from the origin – vector – units: km or m
• Distance – Total distance travelled during journey – scalar – units: km or m
• Speed – How fast an object travels a distance in a period of time – scalar – units: ms^-1 or kmh^-1
• Average – total distance/ time taken
• Instantaneous – speed at a given point in time
• Velocity – how fast an object travels in a given direction – vector – units: ms^-1 or kmh^-1
• Acceleration – rate of change of velocity – vector – unit: ms^-2
• a = (v-u)/t
• a – acceleration (ms^-2)
• v – final velocity (ms^-1)
• u – initial velocity (ms^-1)
• t – time taken (s)

There you have it; the key definitions you need when studying kinematics. As ever, if you have any thoughts, feedback, questions or suggestions please post them in the comments.