 # A Study of Speed, Velocity and Acceleration

## Presentation on theme: "A Study of Speed, Velocity and Acceleration"— Presentation transcript:

A Study of Speed, Velocity and Acceleration
Motion A Study of Speed, Velocity and Acceleration

To describe motion accurately a
FRAME OF REFERENCE is necessary. A FRAME OF REFERENCE is a system of objects that are not moving with respect to one another.

What is Motion? When an object changes position in relation to a FRAME OF REFERENCE (an object that is not moving) we say that the object is in motion For example, a car is in motion when it changes its position with a FRAME OF REFERENCE such as a tree.

When describing motion it is helpful to be able to describe how far an objected moved and which direction the object moved in.

Distance is the length of a path between two points.
The distance of this car traveled on the track is 50 cm.

Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.

Distance and Displacement are similar but not the same.

Distance is either zero
or a positive value.

Displacement uses positive and negative numbers.
Positive numbers are for displacement to the right of the origin & Negative numbers are for displacement to the left the origin.

Distance Vs. Displacement
5 km Distance: how far something actually traveled total (25km) Displacement: the length of the straight line between the starting and stopping points (11km) 10 km 11 km 10 km

Displacement = ? Diner from home is 15 km Total Distance = ?

25km Displacement = 21km 15 km Total Distance = ? 5 km 15 km

Displacement = ? 10 km 5 km Total Distance = ?

How many steps did it take to walk around the room?
Where do you end up on his walk?

Speed Speed describes how fast an object is moving
If an object is not moving it has no speed

Instantaneous speed A speedometer shows a car’s instantaneous speed.
The instantaneous speed is the actual speed an object has at any moment.

When an object is covering an equal distance
in an equal amount of time, it is moving at a constant speed Most objects do not travel at constant speed

When you divide the total distance of a trip by the time taken you get the average speed.
On this driving trip around Chicago, the car traveled and average of 100 km/h.

Speed The speed of a moving object is usually different at any given moment, so we must calculate the average speed Average Speed (V) = Distance (D) Time (T) Units= m/s D V T

distance units over time units.
The units for speed are distance units over time units.

to mean speed with direction.
We use the term velocity to mean speed with direction.

Velocity describes the speed and direction of an object
i.e. The car was moving with a velocity of 25m/s east Velocity (V) = Distance (D) Time (T) Units= m/s + direction

Graphs of Motion Constant speed means the speed stays the same.
An object moving at a constant speed always creates a position vs. time graph that is a straight line.

Speed can be represented in a Position(distance)-time graph

Time is the independent variable because time will pass whether distance is traveled or not

Distance is the dependent variable because the distance traveled depends on how much time an object is moving

A position vs. time graphs can compare the motion of different objects.
The steeper line on a graph means a faster speed.

The slope of a line is the ratio of the “rise” to the “run”.
The steepness of a line is measured by finding its slope. The slope of a line is the ratio of the “rise” to the “run”.

Most objects do not move at a constant speed

Acceleration is the rate at which your speed
(or velocity) changes. If your speed increases by 1 meter per second (m/s) for each second, then your acceleration is 1 m/s per second.

Acceleration occurs whenever there is a change in speed, direction, or both.

The word “acceleration” is used for any change in speed, up or down.
Acceleration can be positive or negative.

Positive acceleration adds more speed each second.
Things get faster. Speed increases over time.

The position vs. time graph is a curve when there is Positive Acceleration.
The car covers more distance each second, so the position vs. time graph gets steeper each second.

Negative acceleration subtracts some speed each second.
Things get slower. People sometimes use the word deceleration to describe slowing down.

When a car is slowing down, the speed decreases so the car covers less distance each second.
The position vs. time graph gets shallower with time.

Acceleration describes how quickly speed changes.
Acceleration is the change in speed divided by the change in time.

Acceleration Acceleration is any change in velocity (a change in speed and/or direction) Acceleration=Final Velocity-Initial Velocity Time a = Vf-Vi t Units= m/s2

(non-zero speed) and have no acceleration (think cruise control).
You can be moving (non-zero speed) and have no acceleration (think cruise control). You can also be accelerating and not moving! A falling object begins accelerating the instant it is released.

An object is in free fall
if it is accelerating due to the force of gravity and no other forces are acting on it.

The letter “g” is used for acceleration due to gravity.
Falling objects increase their speed by 9.8 m/s every second, or 9.8 m/s2 The letter “g” is used for acceleration due to gravity.