PPT Electric Car

Developer Notes

·  The electric cars are neat, but will everyone be able to get them? (You don’t want remote control with variable speed – the transmitters would interfere, and if they didn’t I think it would get out of control – too much fun.)

·  Is there something else we could use in place of the cars? Consistent speed in a straight line, cheap and available. Battery-powered is nice.

·  How to get constant speed in a straight line? Need some stored energy and a controlled release. Batteries tend to be controlled by voltage and resistance in the motor. Otherwise an escapement is good.

·  Clock motor. Easy to get at crafts shops, but enough power to run a car? And how to separate the hour, minute, second hands?

·  Rubber band

·  Clothes pin

·  mouse trap

·  raised weight

·  chemical action

·  solar

·  pendulum and escapement, like a grandfather clock

·  electric cars, tanks, trucks. Joe has found them for about $1, but can anyone else?

·  wobble walkers

·  rocking descending monkey

·  rolling ball bearings don’t work. They slow down to much, and floors aren’t flat.

·  Make an electric car. Motors should be easy to get. Where? Wheels should be easy to get. Where? 3-wheeler with single front driven wheel would be best. Wheel could be right on shaft, but some gearing would be good. Have the shaft press on the wheel to turn it. Have the kids make them? I’m assuming AA batteries. Could make connections with paperclips, thumbtacks. Don’t want to get into electricity in depth at this point. Does every group get to build their own? That means about 13 kits for each class – or else one class gets to build them all.

· 

·  Could go in a circle, like seeing how far a second hand moves, but that introduces rotary motion and pi, so is more complex than necessary.

·  Can we do something with students walking instead of using cars? Except that would get away from the idea of a straight-line graph.

·  They could time average speed to cover a distance.

·  After that they could try to walk at a consistent speed to achieve the same average speed.

·  They could time each other.

·  Could get into trouble with running.

·  Don’t need to buy cars.

·  Should the problem be phrased, “Describe the motion of the car.” Then lead to a discussion of “what can we measure?” & “how fast?”

·  I’ve included a little about independent & dependent variables, but I think this may belong in Dollar drop (sc).

Version / Date / Who / Revisions
04 / 8/6/03 / sc / ·  Added something about ind. & dep variables
·  Added: mks units
·  Added: graph speed vs. time and discussion of having car rolling before timing
·  Mentioned graphing toolsheet
·  Added 5-fold path to students section (should maybe include in teachers???)

1.1.2 ElecCar 04sc.doc Page 5 of 6

dk

PPT Electric Car

Goals

·  Introduce distance, time, and speed.

·  Students should understand the concept of speed and be able to do calculations involving speed, distance, and time.

·  Introduce stopwatches and distance measuring.

·  Introduce the idea of 3 variables.

·  Introduce the idea of creating a new unit out of two existing ones, and of the arbitrariness of creating the new one.

·  Practice graphing, ratios, and dimensional analysis.

Concepts & Skills Introduced

Area / Concepts
Physics / Time
Distance
Speed
Average speed
Instantaneous speed
Lab skills / Stopwatch
Measuring distance
Math / Ratios
Graphing
y=mx
3 variables
(Dimensional analysis)?

Time Required

This whole activity should take about 1 class period

Warm-up Question

Was Cool Papa Bell (a Negro leagues baseball star) really so fast that he could flick a light switch and be in bed before the light went out?

Presentation

Electric cars should be fun to play with. Buy cheap ones that go straight. I suppose you could buy remote control cars, but the remotes will interfere with each other and things will get out of control. Give the cars to the students and ask them to measure how fast the car goes. Tile floors are helpful because students can use the squares to measure distance.

Other materials probably needed:

·  1 stopwatch for each group

·  1 meter stick or metric tape measure for each group

Each group should be taking readings at more than one distance or time. Introduce/review the concepts of independent and dependent variables. The independent variable is the variable you choose to change, while the dependent variable is what changes in response to the independent variable. Let the groups decide on their own what they want as their independent and dependent variables (time or distance).

At some point, discuss what units they use for measuring distance and time. Emphasize SI units. In this course we focus on the “mks” (meters, kilograms, seconds) system. Subsequent formulas rely on using the units of meters, kilograms, and seconds. (Note: there is a “cgs” system of centimeters, grams, and seconds).

When all of the groups are finished collecting data, have a class discussion.

·  What do you need to measure how fast something goes? What units did you use?

·  Graph the data.

·  Is it a straight line?

·  Some groups will have done time/distance and some distance/time. Discuss the difference and get into the arbitrary nature of the definition of speed. Speed is defined as d/t. s=d/t

·  The graph (with time on the x-axis) is a graph of speed. It should be a straight line in this case. y=mx. m is the rate, or ratio of distance and time, or the speed. Or, d=st.

·  Extrapolate the distance for a different time. Interpolate the time for a given distance.

·  Graph speed vs. time. This should produce a horizontal line. Some students may have a graph that starts at (0,0) while others may not. Should it start at (0,0)? It depends- was the car starting from rest? Discuss the timing error involved when starting with the car at rest. If the car is already rolling when timing begins (when the car passes a certain mark), anticipation is minimized and acceleration is not included.

·  ***Do exercises with 3 variables***

The “Graphing Toolsheet” is an excellent introduction to/ review of graphing techniques. This can be assigned before or after the activity, or as needed.

Embedded assessment: Graphing
Are the x- and y- axes labeled and scaled appropriately?
Are the points properly placed on the graph?
Is a relationship identified and a best fit line drawn?
Can they determine the slope of the line?
Background/ History

How fast does something move? Really fast? Really slow? Compared to what? How do you know? How do you measure it? How can you compare? What do you need to know to measure how fast something moves? Let’s take an example and play with it.

Problem

Figure out how fast the electric car moves.

Materials

·  1 electric car for each group

·  (Other materials available if needed)

Procedure

1.  In your groups, plan how you will figure out how fast the car goes.

2.  Perform your test and collect data.

3.  Make sure you have expressed your data/ results in all of the following ways (the order does not matter):

§  Qualitative description/ picture of what’s occurring

§  Data Table

§  Graph

§  Formula

§  Written analysis/summary

Summary

Exercises

For all calculations, show your work and circle your final answer.

Keep the units straight (like km/hr).

  1. The cheetah, the fastest land animal, can travel at a constant rate of 25 m/s for short periods of time. At this speed, what distance will the cheetah cover in 10.0 s?
  1. A woman swims a 1200 meter course in 880 seconds. What is her average speed?
  1. Assuming the woman maintains this speed, how far can she swim in 25 minutes?
  1. A horse pulling a wagon moves at 5 km/hr. How long will it take the horse and wagon to go 50 km?

Challenge/ Extension

1.  Calculate your average speed to (or from) school.

Writing Prompts

·  What is distance?

·  What is time?

·  Why isn’t speed equal to time/distance instead of distance/time?

·  Can you have distance without time?

·  Can you have time without distance?

·  How does instantaneous speed compare to average speed?

1.1.2 ElecCar 04sc.doc Page 5 of 6

dk