8.6B SS - differentiate between speed, velocity, and acceleration

What is the difference between speed, acceleration and velocity?

How is speed calculated? How do we know if something is moving

quickly or slowly? What about the speed of things we can’t see?

(think about internet “speed”) Has our idea of “speed” changed over time?

Usain Bolt blitzed the field once again in the 100m sprint at the Rio Olympics, making it three gold medals in a row in the event.

So how fast can he run? And how does that top speed compare?

Bolt in the 2016 Rio Olympics

Bolt's winning time of 9.81 secs equates to an average speed of 36.7 kmh.

However, that's just an average - his actual top speed is much faster than that.

In 2009 when he set a new world record of 9.58sec, it was calculated that Bolt's speed peaked at 12.27 meters per second or 44.16 kmh. (1 km = .6miles) – he ran 27.3 mph!

Lindsey Vonn – best downhill skier

If you want to be the fastest in the world – you have to understand some basic (and not so basic) physics!

Let’s start by adding to our understanding of how things move

A way to describe motion.

Average speed - Rate of motion calculated by dividing the distance traveled by the amount of time it takes to travel that distance

Constant speed - Speed that does not change

Instantaneous speed - Speed of an object at any given time

Units: Measured in m/s

Acceleration does NOT = speed! It is a change in direction and/or speed, not just

limited to “speeding up” (which is how most people misuse the term).

It can also mean to slow down or change direction.

It sounds strange to us, but physicists will say when the car is slowing down at a stop sign that it is accelerating!

Speed is calculated by dividing distance by time.

Remember – average speed is speed over a given amount of time! So the formula is:

A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?

A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?

Speed = Distance ÷ Time

Speed = 100 m ÷ 20 sSpeed = 5m/s

Remember to include the

UNITS!!

Velocity is speed with direction. Calculating velocity is the same as calculating

speed (distance/time).

The difference is that velocity is what physicists call a vector. A vector means size and direction.

There must be direction. For example:

Speed = 3 m/s

Velocity = 3 m/s, heading northeast

Velocity = Final Distance – Initial Distance

Final Time – Initial Time

Speed describes distance and time

Velocity describes distance, time, and direction

You can say the top speed of an airplane is 300 kilometers per hour (kph). But its velocity is 300 kph in a northeast direction.

A vector is a quantity that has both magnitude (numerical size) and direction.

This is the opposite of a scalar, which is a quantity that only has magnitude and no direction

A simple example is velocity. It has a magnitude, called speed, as well as a direction, like North or Southwest or 10 degrees west of North.

Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity.

An object is accelerating if it is changing its velocity.

If an object is not changing its velocity, then the object is not accelerating.

Acceleration is a change in velocity by

Changing speed – a change is speed could be:

1. Starting

2. Stopping

3. Speeding up

4. Slowing down

Or changing direction

Acceleration can be positive or negative

Speeding Up – Positive acceleration (+)

Slowing Down – Negative acceleration (-)

Units – measured in m/s2

Acceleration is caused by unbalanced forces Calculating Acceleration:

Acceleration = change in velocity that occurs over a certain amount of time

How are they connected? Acceleration is a change in speed, direction or

BOTH! Again, acceleration is simply the measure of

the change in velocity. It occurs when there is a change in speed, direction, or both.

If you kick a soccer ball down the field during a game, the direction of the ball and the speed at which it travels is constantly changing. This means that the acceleration of the ball is continuous as well.

Which of the following sentences contain an example of velocity and which contain an example of speed?

A. Five seconds into the launch, the rocket was shooting upward at 5000 meters per second.

B. Cheetahs can run at 70 miles per hour.

C. Moving at five kilometers per hour, it will take us eight hours to get to the base camp.

D. The car covered 500 kilometers in the first 10 hours of its northward journey.

E. Roger Bannister was the first person to run one mile in less than four minutes.

Velocity

Velocity

Speed

Speed

Speed

Now that you have filled in the blanks with either “speed” or “velocity”. Go back to the sentences that are examples of velocity. Highlight or underline the key words that make them examples of velocity.

Hint: look for directional words!

Brain Pop Crash Course

To get full credit for each problem, you need to show the first step which is to put the distance (with units) over the time traveled (with units).

Show the answer WITH units!!1. 600 miles – distance, 3 hours is time.If S = d/t then the problem is:S = 600 mi

3 hrs = 200 mi/hr or mph

Work on Speed Machines HW with a partner or independently

DO NOT turn it in if you finish it We will go over it in class next time before

you turn it in.