To Do or Not To Do

- Hey, Professor! When you were saying that there was homework, did you mean that we had to do it?

I needed a moment to comprehend that question.  

Dear Student, I designed and posted the HW assignment just because I like to post something from time to time and apparently I did not have anything better to do yesterday.  

An end-of-semester message

No kidding!

Relativity of Time

Where physics meets philosophy... There is another view on the relativity of time: 

Growing older is mandatory.  

Growing up is optional.

Just a thought dedicated to my students.

Torque

The picture above shows two masses in an equilibrium. Physicists see this situation through the lenses of forces and their respective arms (an arm is the distance from pivot point to the point where the force is exerted).

 counterclockwise torque (the left side) = 26 cm * 100 g = 2600 cm*g

clockwise torque (the right side) = 13 cm * 200 g = 2600 cm*g

Accelerated motion

The time of glider passing between photogates is measured with high accuracy (0.001 s). 

The same video in low motion:

Distance in accelerated motion

The air track is elevated (see its right leg in the picture), so the observed motion is accelerated due to gravity. Two photogates allow to measure the time needed to move between them with high accuracy. In our experiment the second photogate was placed each time 10 cm farther to the left (see the data below). 

(Graph by Tim)

Speed in accelerated motion

The glider blocks the photogate passing through. If the glider's flag is 10 cm long and the measured time is 0.214, then the speed of the glider is

v = l / t

v = 0.1 m / 0.2157 s = 0.4636 m/s

Once again, now in slow motion:

Speed in accelerated motion

The photogate measures time of the glider passing through. To calculate its speed, use the length of glider's flag. Moving the photogate farther allows to measure the increasing glider's speed:

v = l / t

l = 10 cm = 0.1 m.

(Graph by Tim)

The graph shows that speed increases at the same rate.

Uniform motion

This setup was used to determine the change in position of the glider in time in the uniform motion. Below there is a graphical representation of the findings.

The graph was done in Excel. Slope of the regression line represents the actual speed of the glider.

(Zuzan's work)

Celsius vs. Fahrenheit (°C vs. °F)

The thermometer shown in the picture gives readings in both degree Celsius and Fahrenheit. The same temperature can be measured using either one of them. Countries that use the metric system, including Canada, use the Celsius scale; in the US we use degree Fahrenheit. This thermometer was bought at the border.

Celsius scale:

water freezes at 0° and boils at 100°. 

Fahrenheit scale:

water freezes at 32° and boils at 212°.

- 40 °F = - 40 °C

You can convert degree Fahrenheit to Celsius and Celsius to Fahrenheit. Here are the formulas:

°C = (°F - 32) * 5/9

°F = °C * 9/5 + 32

Physics I. Help me!

About electricity

ELECTRICITY, n. The power that causes all natural phenomena not known to be caused by something else. It is the same thing as lightning, and its famous attempt to strike Dr. Franklin is one of the most picturesque incidents in that great and good man's career. [...] Electricity seems destined to play a most important part in the arts and industries. The question of its economical application to some purposes is still unsettled, but experiment has already proved that it will propel a street car better than a gas jet and give more light than a horse.

The Devil's Dictionary

This is funny definition of gravitation

GRAVITATION, n. The tendency of all bodies to approach one another with a strength proportion to the quantity of matter they contain - the quantity of matter they contain being ascertained by the strength of their tendency to approach one another. This is a lovely and edifying illustration of how science, having made A the proof of B, makes B the proof of A.

The Devil's Dictionary

Thomas Edison

Did you know that...

New Jersey
is home to more scientists and engineers per square mile
than anywhere else in the world.

 (The Official Website for the State of New Jersey, "2001")

The most interesting interpretations of an image construction diagram

One needs just two rays to find an image of an object formed by a diverging lens.  Below, there are the most interesting interpretations of constructing the diagram. I admire creativity expressed in these works.