Studio Session 3

Newton's laws

Today you will perform a series of experiments that demonstrate Newton's laws of motion.

Equipment needed:

Open a Microsoft Word document to keep a log of your experimental procedures and your results.  This log will form the basis of your studio session report.  Address the points highlighted in blue.  Answer all questions.

Newton's 1st Law

"When viewed in an inertial reference frame, an object at rest remains at rest and an object in motion continues in motion with constant velocity unless it is acted on by an external net force."

Assume that you sitting in your stopped car with your seatbelt fastened waiting for a green light.  Another car suddenly hits your car from behind.  After recovering from the surprise, you notice a pain in your head and neck.

Now assume you are a passenger in a moving car and this car hits the back of a stopped car.

Experiment 1

Place a ball on a book that you hold out in front of you like a tray with one hand.  Record what happens to the ball when you conduct the following three experiments.

Are your observations consistent with Newton's first law?  Discuss!

Reconsider the situation where a stopped car is hit from behind by a moving car. 


Newton's 2nd law

Experiment 2

Step through 4 video clips frame by frame.  The clips show a cart on a track.  An Pasco wireless force and acceleration sensor is attached to the cart.  A force is applied to the force sensor by a falling weight, and the computer screen displays the output of the force and acceleration sensors as the cart accelerates.  The pulling force measured by the force sensor is approximately equal to the net force acting on the cart.


Open Microsoft Excel and record the average readings of the force (N) and acceleration (m/s2) sensors in a table. (The readings may vary a little from frame to frame. Find a reasonable average.))

a (m/s2) F (N)

Produce a graph of force versus acceleration. 
Give the graph a title and label the axes.
The label for the x-axis should be "a (m/s2)", and the label for the y-axis should be "F (N)".

Paste your graph into your log.  Refer to your graph and describe the relationship between force and acceleration using words. 

Right-click your data and choose "Add Trendline".  Choose "Type, Linear" and "Options, Set Intercept 0, Display equation on chart".  An equation y = ax will appear on your graph, where the number a is the slope.  What is the physical meaning of the slope?

Write down Newton's 2nd law in the form of an equation.  Define any variables and/or constants.  What is your best estimate for the mass of the cart and the sensors in the video clips?


An elevator ride

The acceleration of the old elevator in the Nielsen Physics Building was measured as it traveled from the second to the sixth floor, starting from rest.  The data were taken using the acceleration sensor in a cell phone.

Open the linked Excel Spreadsheet.

Discuss with your partners what these graphs tell you.  Explain in detail how to relate the information in the graphs to a ride in an elevator.

Newton's 3rd Law

Experiment 3

Before you leave, please plug the USB force sensor into a USB port of a computer to keep it fully charged for the next group of students.

Convert your log into a session report, certify with you signature that you have actively participated, and hand it to your instructor.