Forest PHYS100 Demos Week1
PHYS 100 Week 1 Demos
Scientific method
Two ball of differnt mass are dropped.
Student compose of theory of which one will hit the ground first.
Measurement
Have the class measure the fall time of an object.
The instructor graphs their times after one measurement.
Then graph the average time from each student measured using 10 trials.
Demo I: The Scientific Method To begin this demonstration I will pass around the medicine ball and the tennis ball so the students can clearly feel the difference in weight. I will then ask them when dropped simultaneously, which ball will hit the ground first. I will call on some students to provide and answer with a reason as to why they believe in their answer (make a hypothesis). We will then proceed to the experiment. I will drop the balls and they will hit the ground at the same time. We will then proceed to the data analysis. I can drop the balls several times so the students can see it wasn’t just a coincidence. We will then analyze the experiment. I can solve the equation of motion for a falling projectile with no initial velocity and show them that there is no mass dependence. Then as a class, we will discuss the results and clear up any questions that may be around. Calculation for Demo I: y= v_0 t+ 1/2 gt^2 →t= √(2y/g) Note there is no mass dependence on the time of flight.
Demo II: Units and Measurements
To begin this demonstration I will pass around some 5kg masses. I will call on some students to make a guess as to how much the mass weighs in Newtons and in pounds. Then I will demonstrate to the students how to convert mass to Newtons, and then Newtons to pounds.
If we have 5kg,then we have 5×9.8=49N
The conversion from Newtons to pounds is 1N= .224 lbs.So if we have 49N then we will get
49N × .224 lbs/N= 10.98lbs
Now that I have shown the students how to do some basic conversions, I will tell them that I am 6’ 1’’ and ask them what that is in meters and centimeters. I will write that there are .3048 meters per foot and 2.54cm per inch. So if I am 6’1’’, then I am 6 feet x .3048 meters/foot = 1.8288 meters and 2.54 cm tall.
Demo III: Error and Accuracy
First I will make sure that everyone has some way of finding the time of flight for the dropping tennis ball (cell phone/stopwatch), and then I will drop the tennis ball from one meter once and create a histogram for the times that have appeared. Also I can explain what a histogram is if the students don’t already know. I will then ask the students to compute the average time that it took the tennis ball to fall. I will make comments on the (hopefully) Gaussian distribution of the times and comment on the width. Since we don’t have very many data points, we will get a wide distribution. Then I will tell the students that I will be repeating this 10 times and that they will all get 10 data points and find the average. Those averages will then be put into a histogram and the distribution should sharpen. I will then explain how more data points leads to a better measurement overall. After I have made a histogram I will compute how long the ball should take to fall theoretically and compare that answer to the times that we have measured. I can then ask the students about the precision of their measurements and the accuracy (If you don’t explain the difference then I can). The theoretical time of flight is t = .45 seconds