Third Laboratory Experiments

Name:_____________________________________________________________

I. Human Reaction Time Measurements:

In this experiment you will measure the reaction time of your laboratory partner. You will do this by dropping a ruler between your lab partner’s fingers and measuring how far it falls before he/she can grab it.

Have your lab partner place her/his thumb and first finger about one inch apart.
Hold a ruler above the thumb and first finger, and let it fall.
Your lab partner is to grab the ruler as fast as she/he can after you let the ruler fall.
On the ruler, read how far it fell before your lab partner caught it. Use centimeters.
Repeat the drop 4 or 5 times and record your data below:

____________, ____________, ______________, ____________, ___________

What is the average distance that the ruler fell? _____________________

Using the equation d = (g/2) t², where g = 980 cm/s², determine the reaction time of your lab partner. Show your work below:

Reaction time = ________________________

Write your answer on the board in front of the class for comparison with the other students.

II Human Pressure on the ground

In this experiment you will measure the pressure on the ground due to your feet while standing.

Stand on the graph paper supplied in class and trace out the pattern of your shoe.
Determine the area of your shoe by counting the squares inside your pattern and multiplying by the area of one square.
Using an estimate of your weight, determine the pressure due to your weight on the ground in units of either pounds/in² or N/m².

Area = ______________________ Pressure = _______________________

III. Human Power

In this experiment you will determine an estimate of your aerobic power and maximum power while going up stairs.

Bring a 2 meter ruler and a stop watch to the stairwell down the hall from our classroom.
Measure how high the stairs rise from the ground floor to the first floor.
Measure the time it takes to walk up at a comfortable pace, aerobically, from the ground floor to the first floor.
Now time how fast you can run up the stairs (maximum power) from the ground to the first floor.

Height of stairs = ________________________________

Time for aerobic walk = _______________________________

Time for run = ______________________________________

Using power = work/time, and that work = force x distance (i.e. weight x height), determine your power output for both aerobic walking and running. Show your work here:

Total work = ___________________________________________________

Aerobic Power = ___________________________________________

Maximum Power = __________________________________________

If you were to walk up stairs for 30 minutes, how many food calories would you burn? Assume that the body is 15% efficient.

IV. Lenses

In this exercise you will experiment with lenses by producing different sized images. The light bench at your table will able to hold a lens and a glass plate on which an image will be formed. You will be given two lenses, one will be thicker in the middle than the other.

a) Finding the focal length of the thicker lens: Parallel light hitting the lens will focus at a point on the other side of the lens. Place the lens in the holder, and the holder as far away as possible from the light source. Focus the image on the screen. Measure the distance from the lens to the image. This distance is (approximately) the focal length of the lens.

Focal Length of thick lens: _____________________________________________

b) Move the lens and screen to form an image that is smaller than the object.

Distance of object to lens: ___________________________________

Distance of image to lens: ___________________________________

c) Move the lens and screen to form an image that is larger than the object

Distance of object to lens:____________________________________

Distance of image to lens: ____________________________________

d) Finding the focal length of the thinner lens: Repeat part a) for the thin lens.

Focal Length of thick lens: _____________________________________________

b) Move the lens and screen to form an image that is smaller than the object.

Distance of object to lens: ___________________________________

Distance of image to lens: ___________________________________

c) Move the lens and screen to form an image that is larger than the object

Distance of object to lens:____________________________________

Distance of image to lens: ____________________________________

V. Atomic Spectra

In this experiment you will examine the light given off by different sources. You will be supplied with a diffraction grating to help determine which colors are given off by the different sources.

1. Use the diffraction grating and examine the light emitted by the tungsten filament (incandescent light source) and one of the atomic sources (florescent light source). What is the main difference in the color spectra given off by these two types of sources? Comment:

2. Using the diffraction grating and the spectrum chart, determine what elements are used in the various atomic sources in the room.

Source 1 =

Source 2 =

Source 3 =

VI. Electric Motors

In this experiment, you will use Doug Johnson’s motor. Each lab desk will be given a motor base with battery. You will make the motor armature, and see how fast it can spin.

Following the example shown in class, make your own armature by coiling transformer wire.
Using sand paper, sand the appropriate parts of the transformer wire. Be sure to use the sand paper on the cardboard supplied to avoid damage to the tabletop!

3. Test out your armature to see how fast it spins. Keep experimenting until your armature spins as fast as it can.

Try to maximize the speed with different armature designs.

What happens to the direction of rotation of the armature if you turn the magnet around?

What happens to the direction of rotation of the armature if you turn the battery around?