Forces Lab
INTRODUCTION
Newton’s Laws of Motion state:
 Newton’s 1st Law: An object at rest stays at rest and an object in motion stays in
motion with the same speed and in the same direction unless acted upon by an
unbalanced force.

Newton’s 2nd Law: The acceleration of an object is directly proportional to the
net force acting on it and inversely proportional to its mass.

Newton’s 3rd Law: If object 1 and object 2 interact, the force exerted by object 1
on object 2 is equal in magnitude but opposite in direction to the force exerted by
object 2 and object 1. (For every action, there is an equal and opposite reaction).
PART A: OBJECTIVES – HOVERCRAFT LAB
 Based on Newton’s Laws of Motion examine the behavior of objects in a
frictionless or friction-reduced environment?

When pushing over a set distance, determine the force applied to the manned
hovercraft at the point of release.

Determine the force of resistance after the point of release.
PART B: OBJECTIVES – COEFFICIENT OF STATIC AND KINETIC FRICTION
 Use a Dual-Range Force Sensor to measure the force of static friction.

Use a Dual-Range Force Sensor to measure the force of kinetic friction

Determine if the coefficient of kinetic friction depends on weight or speed.
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PART A: PROCEDURE – HOVERCRAFT LAB
Materials and Apparatus
 Logger Pro graphing software
 Hovercraft, vacuum, extension cords (30 meters)
 Eight stopwatches
 Measuring tape
 Masking tape
 Personnel
o One student to ride hovercraft with vacuum (RIDER)
o Two students to catch manned hovercraft beyond the finish line
(CATCHERS)
o Eight students with stopwatches to record time (TIMERS)
o One student or instructor to push manned hovercraft (PUSHER)
o One student to log recorded times (RECORDER)
Procedure
1 Choose a surface that is “smooth” and “flat” (i.e. school hallway) with at least 40
meters of distance.
2 Designate a starting point (0-meter marker) with tape. This point represents the
starting line or origin.
3 Using measuring tape, place tape on the ground at 3-meter intervals for 24 meters.
4 The TIMERS will be placed at each tape marker with a stopwatch. Do not place a
student 0-meter tape marker.
5 The CATCHERS will be placed 2 – 3 meters beyond the finishing line to gently
slow down hovercraft at end of trip.
6 The PUSHER will start from an exact distance of 15 meters in front of the starting
line. Use measuring tape to get exact distance in front of starting line.
7 The RIDER will get on hovercraft with vacuum. The instructor will make sure
the RIDER is situated properly on the hovercraft. The instructor will turn the
hovercraft “on” and move the RIDER into a resting position exactly 15 meters in
front of the starting line.
8 Once in position 15 meters in front of starting line, the PUSHER with push the
RIDER towards the starting line.
9 Once the RIDER and the front of the hovercraft reach the first tape marker, the
PUSHER will release the RIDER from their hands and simultaneously yell
“start”.
10 Once the PUSHER yells “start”, the TIMERS will simultaneously start their
stopwatches. As the front of the hovercraft passes each tape marker the TIMERS
will stop their stopwatches.
11 The RECORDER will log the times at each tape marker and note the name of the
RIDER.
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PART A: DATA TABLE #1: “WIND UP / CHAPTER #1”
Trial
Initial
Velocity
(m/s)
1
0
2
0
3
0
4
0
5
0
6
0
7
0
8
0
9
0
10
0
Time
(s)
Displ
(m)
Accel
(m/s2)
3
Final
Velocity
(m/s)
Total
Mass
(kg)
Force
Applied
(N)
PART A: DATA TABLE #2: “COASTING / CHAPTER #2”
Trial
Initial
Velocity
(m/s)
Time
(s)
Displ
(m)
Accel
(m/s2)
1
2
3
4
5
6
7
8
9
10
4
Final
Velocity
(m/s)
Total
Mass
(kg)
Force
Resistance
(N)
PART A: ANALYSIS
1. Calculate the following during the “wind-up”: (Show work for one trial and
answers for each other trial)
 Acceleration
 Final velocity
 Force applied
2. Calculate the following during the “coasting”: (Show work for one trial and
answers for each other trial)
 Acceleration
 Final velocity
 Force of resistance
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PART B: OBJECTIVES – COEFFICIENT OF STATIC AND KINETIC FRICTION
MATERIALS
Computer
Vernier computer interface
Logger Pro
Vernier Motion Detector
Vernier Force Sensor
String
block of wood with hook
balance or scale
mass set
PART B: PROCEDURE – COEFFICIENT OF STATIC AND KINETIC FRICTION
Part I Starting Friction
1. Measure the mass of the block and record it in the data table.
2. Connect the Dual-Range Force Sensor to Channel 1 of the interface. Set the range
switch on the Force Sensor to 50 N.
3. Open the file “12a Static Kinetic Frict” from the Physics with Vernier folder.
4. Tie one end of a string to the hook on the Force Sensor and the other end to the hook
on the wooden block. Place a total of 1 kg mass on top of the block, fastened so the
masses cannot shift. Practice pulling the block and masses with the Force Sensor
using this straight-line motion: Slowly and gently pull horizontally with a small force.
Very gradually, taking one full second, increase the force until the block starts to
slide, and then keep the block moving at a constant speed for another second.
5. Sketch a graph of force vs. time for the force you felt on your hand. Label the portion
of the graph corresponding to the block at rest, the time when the block just started to
move, and the time when the block was moving at constant speed.
6. Hold the Force Sensor in position, ready to pull the block, but with no tension in the
string. Click
to set the Force Sensor to zero.
7. Click
to begin collecting data. Pull the block as before, taking care to increase
the force gradually. Repeat the process as needed until you have a graph that reflects
the desired motion, including pulling the block at constant speed once it begins
moving. Print or copy the graph for use in the Analysis portion of this activity.
Part II and III Peak Static Friction and Kinetic Friction
In this section, you will measure the peak static friction force and the kinetic friction
force as a function of the normal force on the block. In each run, you will pull the
block as before, but by changing the masses on the block, you will vary the normal
force on the block.
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Mass
Wooden block
Dual-Range
Force Sensor
Pull
Figure 1
8. Remove all masses from the block.
9. Click
to begin collecting data and pull as before to gather force vs. time data.
10. Examine the data by clicking the Statistics button, . The maximum value of the
force occurs when the block started to slide. Read this value of the maximum force of
static friction from the floating box and record the number in your data table.
11. Drag across the region of the graph corresponding to the block moving at constant
velocity. Click on the Statistics button again and read the average (or mean) force
during the time interval. This force is the magnitude of the kinetic frictional force.
12. Repeat Steps 9-11 for two more measurements and average the results to determine
the reliability of your measurements. Record the values in the data table.
13. Add masses totaling 250 g to the block. Repeat Steps 9–12, recording values in the
data table.
14. Repeat for additional masses of 500, 750, and 1000 g. Record values in your data
table.
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PART B: DATA TABLE #1 – COEFFICIENT OF STATIC AND KINETIC FRICTION
Part I Starting Friction
Mass of block
Kg
Part II Peak Static Friction
Total
mass
(kg)
Normal
force
(N)
Peak static friction
Trial 1
Trial 2
Trial 3
Average
peak static
friction
(N)
S
Part III Peak Kinetic Friction
Total
mass
(kg)
Normal
force
(N)
Kinetic friction
Trial 1
Trial 2
Trial 3
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Average
kinetic
friction
(N)
K
PART B: ANALYSIS – COEFFICIENT OF STATIC AND KINETIC FRICTION
1. For part II, calculate the following: (Show work for one trial and answers for each
other trial)
 Average peak static friction
 Coefficient of static friction
2. For part II, calculate the following: (Show work for one trial and answers for each
other trial)
 Average peak kinetic friction
 Coefficient of kinetic friction
3. Does the coefficient of kinetic friction depend on speed?
4. Does the force of kinetic friction depend on the weight of the block?
5. Does the coefficient of kinetic friction depend on the weight of the block?
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