Reduced Gravity
Flight Team

ACC REGIONAL COLLABORATIVE

"PHYSICS EXPERIMENT ON FRICTION"

 

I. INTRODUCTION

The objective of this activity is to measure the maximum static friction force and the kinetic friction force. The maximum static friction force f s,max is the friction force acting on the object at the instant of impending motion. It is equal to the minimum force required to get the object to move. The kinetic friction force is the friction force exerted on the object by the table when the object is moving (sliding) with steady speed.

 

II. KEY CONCEPTS

 

1. Force is the push or pull of one object on another object.

 

2. Aforceisa directional quantity. It has a magnitude such as 5.00 lb and a direction.

 

3. Weight is a force. It is the most important force acting on us. The weight of a person is the earth’s gravitational pull on that person.

 

4. In the SI (metric) system, the unit of force is the Newton, abbreviated N. In the USCS (United States Customary System), the unit of force is the pound (lb). 1.00 lb = 4.45 N.

 

5. Mass is the quantity of matter in an object. It is a measure of its inertia. It is the object’s ability to resist change in its state of motion. The weight of an object is proportional to its mass

 

Weight = mass • acceleration of gravity or W = mg

 

III. PREDICTION:

With your lab group, try to predict the relationship between the friction force on an object and its weight. Does it take a larger force to drag a heavy object on a table as opposed to a lighter object? Do you think there will be a proportionality between the force needed to get the object to budge and its weight? What about the force needed to get the object to move with steady speed and the weight of the object?


 

IV. APPARATUS:

Wooden box, masses, spring balance.

 

V. PROCEDURE:

 

1. Place the wooden box on the digital scale and read its mass in grams. Convert to kilograms. 1.00 kg = 1000 g. Record all data in the data table.

 

2. Hook up the spring balance to the wooden box and carefully increase your pull until the box starts to move. Be ready to read the spring balance at the instant of motion. At this instant, the force of the spring balance (which is really your pull) is equal to the maximum static friction force. Continue pulling on the box steadily as the box moves with a steady speed and read the force of the spring balance. This force is the kinetic friction force.

 

3. Repeat the above step four more times each time increasing the mass in the box by 0.200 kg and read the maximum static friction force and the kinetic friction force.

 

 

VI. ANALYSIS:

 

1. Plot the maximum static friction force on the vertical axis and the weight on the horizontal axis. Draw the "best straight line fit" for the data and calculate the slope of the line. The slope of the line is a physically meaningful quantity for this experiment.

 

2. Write a conclusion summarizing your results. Does your prediction agree with your results?

 

 

Text Box: 		Friction Force Data Table 	  Mass Kilograms (kg) 	Weight W = mg (N) 		Fs,max (N) 	Fkinetic (N)

ACC REGIONAL COLLABORATIVE MEASUREMENT OF THE ACCELERATION OF GRAVITY

 

I. OBJECTIVE

The objective of this experiment is to measure the acceleration of gravity, g, by studying the motion of a freely-falling object. This will be done using a free-fall apparatus with a spark timer which will record the vertical position of a freely-falling object and the elapsed time. The measured g will be compared to the ac­cepted value of 9.80 m/s 2 .

 

II. KEY CONCEPTS

 

1. Displacement of an object is the change in its position.

 

Displacement = position two − position one

 

2. Velocity of an object is its displacement divided by the time for the displace­ment to take place.

 

 

displacement

Velocity =

time interval

3. Acceleration is the change in velocity divided by the time interval. It is the rate of speeding up or slowing down.

 

change in velocity

Acceleration =

time interval

 

4. An object is in free fall if it is moving under the action of the earth’s gravity only. When your pencil drops to the floor, it is in free fall.

 

5. Acceleration of gravity is the rate of change (increase or decrease) of the velocity of a freely-falling object.

 

 

III. PREDICTION

With your lab group, try to predict as much as you can about the acceleration of gravity. Helpful questions to ponder: Do heavy objects fall to the ground at the same rate as light objects? Neglecting air resistance, if you drop a feather and a metal ball from the same height, do they hit the ground at the same time?


 

II. APPARATUS

Behr free-fall apparatus with spark timer, waxed paper tape, plumb bob, and a ruler.

 

IV EXPERIMENTAL PROCEDURE

 

1. The lab assistant will run the free-fall apparatus with spark timer and pro­duce a waxed paper tape which has a distance vs. time record of the motion of the falling object. This tape will be given to you to analyze the free-fall motion. Note: The spark timer sparks 30 times per second.

 

2. Place the paper tape on the lab table and tape it. The position of the object is represented by sparks along the length of the tape. These sparks occur at equal time intervals but not equal distance intervals. Question: Why do you think the sparks are not equally spaced? Answer:

 

3. Neglect the first couple of sparks at the beginning of the tape due to the fact that they are very close to each other and measuring the distance between them is difficult. Then select two sparks near the beginning of the motion, measure the distance between them to the nearest millimeter mm.

 

4. Calculate the average velocity of the spark timer in this interval. Call this velocity v 1 . Record your data and do the calculations and enter the result in the data table.

 

5. Select two sparks near the middle of the motion and repeat your measure­ment and calculation as you have done above. Call this velocity v 2 .

 

6. Select two sparks near the end of the motion and repeat your measurement and calculation as you have done above. Call this velocity v 3 .

 

 

V. ANALYSIS

1. Calculate the acceleration of gravity from v 1 and v 2 .

 

 

acceleration of gravity =

v 2 − v 1

the appropriate time interval

 

2. Calculate the acceleration of gravity from v 2 and v 3 .

 

 

acceleration of gravity =

v 3 − v 2

the appropriate time interval

 

3. Within the accuracy of this experiment, are the two accelerations the same? You can take their average as your measurement for the acceleration of grav­ity.

 

4. Calculate the percent difference between the measured value of the accelera­tion of gravity and the accepted value of 9.8 m/s 2 .

 

% difference=

|slope − 9.80 |

 

• 100 (1)

 

9.80

 

5. Write a conclusion summarizing your results. Comment on the success of this experiment. What do you think are the two most important sources of error?

Acceleration of Gravity Data Table

Distance between

Time Interval

Average Velocity

Sparks

seconds (s)

(m/s)

(m) 0.0333

v 1 = 0.0333

v 2 = 0.0333

v 3 =

Acceleration of Gravity Data Table

Acceleration of Time Interval

gravity seconds (s)

v 2

v 1

( m/s )

( m/s )

g

( m/s 2 )



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