Speed1.3 pp. 17-21

Mr. Richter

Agenda

Warm-Up

Review Pop Quiz

Any Questions from the Lab?

Introduce Speed

Oil Drop Drawing

Notes: Speed Calculating Speed Average Speed Formula Solving Physics Problems

Oil Drop and Distance vs. Time Graph Practice (tomorrow)

Distance, Time and Speed Test on Wed, October 3

Objectives: We Will Be Able To…

Interpret “oil drop” diagrams and distance vs. time graphs.

Define speed.

Express an object’s speed using various units.

Calculate speed, distance, or time given two of the three quantities.

List the steps for solving physics problems.

Warm-Up:

A car has an oil drip. As the car moves, it drips oil at a regular rate, leaving a trail of spots on the road.

Which of the following diagrams of the car’s trail of spots shows the car continuously slowing down? How do you know?

Visual Representations of SpeedOil Drop Diagrams and Distance vs. Time Graphs

Group Drawing

At your table, use the whiteboard to show:

1. The oil drop diagram of a car that starts fast, slows down, then speeds up again.

2. Copy the diagram that represents the best representation into your notes.

3. Now, draw the distance vs. time graph of the same car.

4. Copy the graph that represents the best representation into your notes.

Diagrams (of Fast, Slow, Fast)

Oil Drop Distance vs. Time

Dis

tance

Time

Speed

What is Speed?

What do you think speed is? Discuss for one minute at your table, and then we will discuss as a class.

Speed: the distance traveled divided by the time it takes.

Constant Speed: the same distance is traveled every second. In physics, the word constant means unchanging (but not

necessarily zero).

What is Speed?

We will usually see speed in the units of meters per second [m/s]. But what does this really mean?

Let’s examine the speed of 3 m/s. This says that for every second that passes (elapses), 3 meters are added to the distance. Like: 1 second, 3 meters 2 seconds, 6 meters 3 seconds, 9 meters 10 seconds, 30 meters

Speed in m/s says that “this many meters are traveled each second”.

Calculating Speed

Speed is a measure of the distance traveled in a given amount of time, so to calculate speed you need to know: distance traveled by the object time it took to travel that distance

“Per” means “for each” and also “divided by”. For example 100 km/h means: 100 km are traveled for each hour that passes, and

Average Speed Formulas

Your Text Book MCAS

Solving Physics ProblemsA Four- (but really Five-) Step Approach

How to Solve Physics Problems

Steps

1. What do you want to find?

2. What do you know?

3. Identify useful relationships. (What formula do I use?)

4. Solve the problem

5. Check your answer. For calculations and realism!

Example

1. v = ?

2. t = 2 seconds, d = 10 meters

3. v = d/t

4. v = 10m/ 2s = 5 m/s

5. “If I go 5 m/s, will I go 10 m in 2 sec? Yes!”

Practice

Look at the example problem on p. 21.

Now, go through the problem solving steps for problems a and b.

The answers are provided, so you should know whether or not you’re doing things correctly.

Wrap-Up: Did we meet our objectives?

Homework

Due Monday: p21 #1-5