Distance, Displacement, Velocity, Speed and Acceleration



Distance, Displacement, Velocity, Speed and Acceleration

Distance and Displacement

Distance is the total path length traveled from one location to another. It is a scalar quantity.

Displacement is the distance between two locations measured along the shortest path connecting them. The SI unit of distance and displacement is meter (m).

Motion: a change in position, measured by distance and time. 

Frame of reference: the point from which movement is determined.

• To measure movement, some point must be considered as nonmoving.

• Earth is the most common frame of reference.

Speed and Velocity

Speed is the distance traveled per unit time or the rate of change of distance.

Speed = total distance traveled / time taken

Velocity is the speed in a given direction or the rate of change of displacement.

Average velocity: In 8th grade we will not be dealing with the direction aspect of velocity and therefore can be calculated just like speed. To put it another way, all our calculations will be about objects moving in a straight line.

Acceleration and Deceleration

Acceleration is the rate of change of velocity.

Acceleration = change of velocity / time taken

Change of velocity = final velocity (v) – initial velocity (u)

Acceleration = (final velocity – initial velocity) / time taken  = (Vf – Vi) / t

Deceleration: A term commonly used to mean a decrease in speed.

Things to remember about acceleration:

1. Constant velocity means the object is not accelerating. Acceleration is zero.

2. Constant acceleration means the object is increasing its velocity.

3. When calculating acceleration, a negative number means the object was slowing down/decelerating.

Force: Defined as a push or pull.

• Forces give energy to objects.

• Forces cause a change in motion.

Friction: a force that opposes motion.

Gravity: the force of attraction between all objects in the universe. 

• Gravity is the weakest of the known natural forces, only becoming obvious when massive objects like stars and planets are involved.

• Gravitational forces between objects increase as the masses of the objects increases.

Gravitational forces between objects increase as the distance between objects decreases

Weight: the effect of gravity on an objects’ mass

Free fall is an object falling under the influence of gravity.

• Near the surface of the earth all objects are accelerated by gravity at a rate of 9.8 meters per second per second or 9.8m/s2

• All object are affected equally by gravity

• The reason some objects fall faster than others is NOT because they are heavier but because of Air Resistance.

• Air resistance depends on the combination of the speed of the falling object, the weight of the object and the surface area of the falling object

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