Physics 125 – Mesa College
Page 1 of 9
Your Name:
Group Name:
Lab Day:
Objective: To understand the relationship between force, mass and acceleration; To create and interpret graphs of these relationships; To evaluate the validity of Newton’s
Second Law for a system with constant acceleration.
Hypothesis: An object accelerates when a net force is applied to it. We assume a net force is present if an object accelerates while observed from an inertial reference frame. We assume that the effects of the earth’s curvature, atmosphere and rotation are minimal.
Mathematical Models and Reference Values Used: Newton’s ‘Laws’ state that acceleration of an object s the result of the net external force acting on it.
F = m

.
The reason not all objects accelerate the same is due to the property of inertia, which is expressed by the mass of the object. Large masses accelerate less than small masses for the same external force. Objects connected to each other by strings or rods will display the same acceleration. Forces are vector quantities and obey vector relationships. Forces acting on an object can be graphically represented by a ‘Free Body Diagram’. A force of one Newton has been defined as the force causing a 1 kg object to accelerate at the rate of 1 m/s 2 .
Equipment List: Air Track & Blower, Glider, Glider Accessory Kit, Photogate, 1&2 Meter
Sticks.
Setup and Procedure
Never move the glider along the track unless the blower is running!
1. Place the glider in the middle of the track and turn on the blower. If the track is level, the glider should remain motionless or gently drift back and forth near the middle of the track. If the glider moves towards one end of the track, level the air track by adjusting the screws in each leg. If this step is not properly completed the experiment will show large errors. Once the track is leveled, turn off the blower.
2. Measure and record the length of the glider flag in Data Table One.
3. Insert the flag into the glider and determine the mass of the glider-flag combination using the electronic balance. Record the result in Data Table One as ‘M o
’.
4. Place a ’50-gram’ mass on each peg on the side of the glider. Record the mass of the glider, flag and masses in Data Table One as ‘M
1
’.
5. Use the electronic balance to measure the value of the empty mass hanger, and record it in Data Table One as ‘m’.
6. Make sure the glider flag can pass under/through the photogate without hitting it.
7. Insert a pulley into the lower opening of the stop at the end of the track. Cut a length of string that will reach from the floor, over the pulley and to the middle of the track.
Revised COM 01/2013

Physics 125 – Mesa College Page 2 of 9
8. Attach the mass hanger to the end of the string near the floor. With the hanger touching the floor, run the string over the pulley and along the track. Attach it to the stem of the glider flag. Lift and reposition the glider on the track until the string is taut, but the hanger is still resting on the floor. The string should be parallel to the track.
9. Use the scale on the side of the air track to determine the position of the leading edge of the glider. You may now want to adjust the length of the string to make this a convenient value, making sure that the mass remains on the floor. Once you are satisfied, record this ‘end position’ in Data Table One.
10. Position the photogate just barely beyond the glider flag.
This will ensure that the glider reaches maximum speed before it enters the photogate. We will assume it maintains that speed as it passes through the photogate.
post and the bumper in the upper hole
then the thread will be almost level.
11. Turn on the blower and pull the glider back until the hanging mass is just below the pulley.
You may want to adjust this
Mass hanger sits upright on floor with thread tight position a little bit to obtain a convenient value. The ‘start’ and ‘end’ positions should be no less than 60 cm apart. Once you are satisfied, record this
‘start position’ in Data Table One. Then turn off the blower again.
Blower and hose
(not shown)
Glider with flag
Hook with thread
Photogate
Pulley
Bumper
Airtrack
Hooked
mass
Data Table One
Length of Glider Flag (m) L =
Mass of Glider and Flag (kg) M o
=
M o
plus 2, ‘50-gram’ masses (kg) M
1
=
Mass of hanger (kg)
‘End’ position (m) m = x f
=
‘Start’ position (m)
Distance traveled = |x f
- x o
| x o
=
Δ x =
Revised COM 01/2013

Physics 125 – Mesa College Page 3 of 9
Applying a varying force to a constant mass glider
1. Move the sliding switch on the photogate to the
‘GATE’ position and press the ‘Reset’ button. The display should read all zeros. If it does not, notify the instructor immediately.
2. Measure the masses of the large and small metal and black plastic masses. Record the values in Data
Table Two.
3. Turn on the blower and allow the air to circulate for several seconds. Position the glider and 50-gram masses at the start position you determined.
4. Make sure that the mass hanger is stationary then release the glider. Have one of your lab partners catch the glider after it passes through the photogate. Do not let it bounce back through the photogate, or your data will be useless. A way to avoid accidentally moving the glider as you release it is to hold a ruler in front of the glider, then move it to start the data run.
5. Record the number shown on the photogate in Data Table Three as t
1 button and repeat the procedure. Record this value as t
2 and record it as well.
. Push the reset
. Take the average of these times
6. Follow the format of Data Table Three to repeat steps 4 and 5 with different amounts of mass on the mass hanger.
Data Table Two
Mass Description
Small black plastic
Reference Label
A
Mass (kg)
Large black plastic
Small metal
Large metal
B
C
D
Data Table Three
Hanging mass (kg) t
1
(s) t
2
(s) t average
(s) Mass Description
Hanger only
Hanger & B
Hanger, B & A
Hanger & C
Hanger, C & B
Hanger & D
Revised COM 01/2013

Physics 125 – Mesa College Page 4 of 9
Q1. Use the data you have taken to fill out Data Table Four. In the space below show a sample calculation for the final speed and the average acceleration of the glider. Show all work with units.
Mass
Description
Hanger only
Hanger & B
Hanger, B & A
Hanger & C
Hanger, C & B
Hanger & D
Initial speed; v o
0
0
0
0
0
0
Data Table Four
Final speed; v f
L
= t average
Acceleration; a = v
2 f
− v o
2
2 ( )
Q2. Derive the expression for the net external force acting on the glider and show that this is equal to the tension in the string caused by the hanging mass. Start with a free body diagram for the glider and another one for the hanging mass and prove that
F ext
= mMg
(m + M)
= T
.
Revised COM 01/2013

Physics 125 – Mesa College Page 5 of 9
Q3. Use the values for M
1
and m that you measured and use them in F ext
= mMg
(m + M)
= T .
Show your work, with units.
Q4. Calculate the value of T = mg when ‘m’ refers to the empty mass hanger. Show your work with units.
Q5. Calculate the percent difference between the actual tension found in Q4 and the approximate value found in Q5. Show your work with units.
Q6. Is it acceptable to use the approximate value for the tension in the string (Q5) instead of the actual value of the tension in the string (Q4)? Explain your response.
Q7. Use whichever method you prefer to calculate the tension in the string. Show one sample calculation with units, then complete Data Table Five.
Mass Description
Data Table Five
Tension in string (N)
Hanger only
Hanger & B
Hanger, B & A
Hanger, C & B
Hanger & D
Revised COM 01/2013

Physics 125 – Mesa College Page 6 of 9
Applying a constant force to a variable mass glider
Place mass C on the mass hanger. The tension this produces will be the constant external force that acts upon the glider. Transfer this value from Data Table Five to Data Table Six.
1. Remove both ’50-gram’ masses from the glider and place the glider at your start position. Call this M o
.
2. Reset the photogate, make sure the hanging mass is stationary then release the glider.
Do not let the glider bounce back through the photogate.
3. Record the time on the photogate in Data Table Six as t
1
Record the second time as t
2
then repeat the procedure.
then calculate the average time.
4. Replace the glider at the start position and add a single ’50-gram’ mass to the glider.
Place the mass on top of and near the middle of the glider by sliding it underneath the edge of the flag as shown in the diagram. Measure and record the value of this mass in Data
Table Six.
5. For each of the mass configurations shown above, measure and record the value of the masses and take two data runs. Record all data in Data Table Six.
Data Table Six
Constant force acting on glider = F external
= Tension in string =
Glider mass description
M o
M o
+ ‘50 grams’
M o
+ ‘100 grams’
M o
+ ‘150 grams’
M o
+ ‘200 grams’
Glider mass (kg) t
1
(s) t
2
(s) t average
(s)
N
Revised COM 01/2013

Physics 125 – Mesa College Page 7 of 9
Q8. Use the data you have taken to fill out Data Table Seven. In the space below show a sample calculation for the final speed and the average acceleration of the glider. Show all work with units.
Glider mass description
M o
M o
+ ‘50 grams’
M o
+ ‘100 grams’
M o
+ ‘150 grams’
M o
+ ‘200 grams’
Initial speed; v
0
0
0
0
0 o
Data Table Seven
Final speed; v f
L
= t average
Acceleration; a = v
2 f
− v o
2
2 ( )
Q9. Calculate the reciprocal of the glider mass for each case and arrange them from smallest to largest, with 1 being smallest. The reciprocal of a quantity is (1/quantity) or quantity -1
Data Table Eight
Glider mass description Reciprocal Mass (kg -1 ) Rank: 1 - 5
M o
M o
+ ‘50 grams’
M o
+ ‘100 grams’
M o
+ ‘150 grams’
M o
+ ‘200 grams’
Revised COM 01/2013

Physics 125 – Mesa College Page 8 of 9
Graphical Analysis
Please make sure you have read and understood the “How to Draw a Graph” download from the course website before proceeding.
Acceleration ( of the glider ) as a function of net force ( acting on the glider )
Q10. Using a Cartesian coordinate system construct a graph of the acceleration of the glider as a function of the net force applied to it, using Data Tables Four and Five. Draw a best-fit line then calculate the slope on the graph, with units. Transfer your result to Data
Table Nine.
Q11. Use the slope value from Q10 to write the equation of the line suggested by your graph. Ignore any intercept, so your function should have the form y ( x ) = mx .
Acceleration ( of the glider ) as a function of reciprocal mass ( of the glider )
Q12. Using a Cartesian coordinate system construct a graph of the acceleration of the glider as a function of the glider’s reciprocal mass, using Data Tables Seven and Eight.
Draw a best-fit line then calculate the slope on the graph, with units. Transfer your result to Data Table Nine.
Q13. Use the slope value from Q12 to write the equation of the line suggested by your graph. Ignore any intercept, so your function should have the form y ( x ) = mx .
Data Table Nine
Quantity
Q11 slope
Mass of M
1
Q14 slope
Tension of ‘Hanger + C’
Value Units
Q14. Use the Q10 slope value to determine the inertial mass of M
1
(the glider, masses and flag). The inertial mass is a measure of ‘resistance to acceleration’.
Revised COM 01/2013

Physics 125 – Mesa College Page 9 of 9
Q15. Calculate the percent difference between the two ways you determined the mass of the glider/mass/flag system (the graph and the electronic balance). Show all work with units.
Q16. If the result is small, what does this tell you about inertial and gravitational
(electronic balance) masses? If the result is large, what caused this difference and how did it cause the difference to be large?
Q17. Use the Q12 slope value to determine the external force acting on the glider, masses and flag.
Q18. Calculate the percent error between the two ways you determined the external force acting on the glider/mass/flag system (the graph and the tension calculation). Show all work with units.
Q19. If the result is small, what does this tell you about the ability of theory to model reality? If the result is large, what caused this difference and how did it cause the difference to be large?
Revised COM 01/2013