University of University of Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Names:
Section:
FORCE AND MOTION
A vulgar Mechanik can practice what he has been taught or seen done, but if he is in an error he
knows not how to find it out and correct it, and if you put him out of his road, he is at a stand;
whereas he that is able to reason nimbly and judiciously about figure, force and motion, is never
at rest til he gets over every rub.
-Isaac Newton
OBJECTIVES
To develop a method for measuring forces reliably.
To learn how to use a force probe to measure force.
To explore how the motion of an object is related to the forces applied to it.
To find a mathematical relationship between the force applied to an object and its
acceleration.
OVERVIEW
In the previous labs, you have used a motion detector to display position-time, velocity-time, and
acceleration-time graphs of different motions of various objects. You were not concerned about
how you got the objects to move, i.e., what forces (pushes or pulls) acted on the objects. From
your own experiences, you know that force and motion are related in some way. To start your
bicycle moving, you must apply a force to the pedal. To start up your car, you must step on the
accelerator to get the engine to apply a force to the road through the tires.
But exactly how is force related to the quantities you used in the previous lab to describe
motion--position, velocity, and acceleration? In this lab you will pay attention to forces and
how
1
,University of University of Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
they affect motion. You will first develop an idea of a force as a push or a pull. You will learn
how to measure forces. By applying forces to a cart and observing the nature of its resulting
motion graphically with a motion detector, you will come to understand the effects of forces on
motion.
INVESTIGATION 1: MEASURING FORCES
In this investigation you will explore the concept of a constant force and the combination of
forces in one dimension. You can use these concepts to learn how to measure forces with a force
probe. You will need the following materials:
computer-based laboratory system
RealTime Physics Mechanics experiment configuration files
force probe
five identical rubber bands
meter stick
Activity 1-1: How Large Is a Pull?
If you pull on a rubber band attached at one end, you know it will stretch. The more you pull, the
more it stretches. Try it.
1. Attach one end of the rubber band to something on the table that can't move. Also attach
the meter stick to the table. Now stretch the rubber band so it is several centimeters
longer than its relaxed length. Does it always seem to exert the same pull on you each
time it is stretched to the same length? (Most people agree that this is obvious.)
2. Write down the length you have chosen in the space below. This will be your standard
length for future measurements.
Rubber band(s) Standard length of rubber band = cm
3. Attach one end of each of two identical rubber bands to something that can't move
and stretch them together side-by-side to the standard length.
Question 1-1: How does the combined force of two rubber bands compare to what you felt
when only one rubber band was used?
2
, University of University of Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
4. Repeat this comparison of how strong the forces feel with three, four, and five rubber
bands stretched together to the same standard length.
Question 1-2: Suppose you stretched a rubber band to your standard length by pulling on it.
Now you want to create a force six times as large. How could you create such a force?
Question 1-3: Suppose you applied a force with a stretched rubber band one day, and several
days later you wanted to feel the same force or apply it to something. How could you assure that
the forces were the same? Explain.
Question 1-4: Do side-by-side rubber bands provide a convenient way of accurately reproducing
forces of many different sizes? Explain.
You have seen that pulling more rubber bands to the same length requires a larger pull. To be
more precise about the pulls and pushes you are applying, you need a device to measure
forces accurately. The electronic force probe is designed to do this.
Activity 1-2: Measuring Forces With a Force Probe
In this activity you will explore the capability of an electronic force probe as a force measuring
device.
1. Plug the force probe into the computer interface. Display force vs. time axes by
opening the experiment file called Measuring Force (L03A1-2a).
If the sensitivity of your force probe can be adjusted, choose the setting appropriate to the
measurements in this activity (about 0 to 10 N or more).
3
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Names:
Section:
FORCE AND MOTION
A vulgar Mechanik can practice what he has been taught or seen done, but if he is in an error he
knows not how to find it out and correct it, and if you put him out of his road, he is at a stand;
whereas he that is able to reason nimbly and judiciously about figure, force and motion, is never
at rest til he gets over every rub.
-Isaac Newton
OBJECTIVES
To develop a method for measuring forces reliably.
To learn how to use a force probe to measure force.
To explore how the motion of an object is related to the forces applied to it.
To find a mathematical relationship between the force applied to an object and its
acceleration.
OVERVIEW
In the previous labs, you have used a motion detector to display position-time, velocity-time, and
acceleration-time graphs of different motions of various objects. You were not concerned about
how you got the objects to move, i.e., what forces (pushes or pulls) acted on the objects. From
your own experiences, you know that force and motion are related in some way. To start your
bicycle moving, you must apply a force to the pedal. To start up your car, you must step on the
accelerator to get the engine to apply a force to the road through the tires.
But exactly how is force related to the quantities you used in the previous lab to describe
motion--position, velocity, and acceleration? In this lab you will pay attention to forces and
how
1
,University of University of Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
they affect motion. You will first develop an idea of a force as a push or a pull. You will learn
how to measure forces. By applying forces to a cart and observing the nature of its resulting
motion graphically with a motion detector, you will come to understand the effects of forces on
motion.
INVESTIGATION 1: MEASURING FORCES
In this investigation you will explore the concept of a constant force and the combination of
forces in one dimension. You can use these concepts to learn how to measure forces with a force
probe. You will need the following materials:
computer-based laboratory system
RealTime Physics Mechanics experiment configuration files
force probe
five identical rubber bands
meter stick
Activity 1-1: How Large Is a Pull?
If you pull on a rubber band attached at one end, you know it will stretch. The more you pull, the
more it stretches. Try it.
1. Attach one end of the rubber band to something on the table that can't move. Also attach
the meter stick to the table. Now stretch the rubber band so it is several centimeters
longer than its relaxed length. Does it always seem to exert the same pull on you each
time it is stretched to the same length? (Most people agree that this is obvious.)
2. Write down the length you have chosen in the space below. This will be your standard
length for future measurements.
Rubber band(s) Standard length of rubber band = cm
3. Attach one end of each of two identical rubber bands to something that can't move
and stretch them together side-by-side to the standard length.
Question 1-1: How does the combined force of two rubber bands compare to what you felt
when only one rubber band was used?
2
, University of University of Maryland, Baltimore CountyPHYS 111Lab Force and Motion
Maryland, Baltimore CountyPHYS 111Lab Force and Motion
4. Repeat this comparison of how strong the forces feel with three, four, and five rubber
bands stretched together to the same standard length.
Question 1-2: Suppose you stretched a rubber band to your standard length by pulling on it.
Now you want to create a force six times as large. How could you create such a force?
Question 1-3: Suppose you applied a force with a stretched rubber band one day, and several
days later you wanted to feel the same force or apply it to something. How could you assure that
the forces were the same? Explain.
Question 1-4: Do side-by-side rubber bands provide a convenient way of accurately reproducing
forces of many different sizes? Explain.
You have seen that pulling more rubber bands to the same length requires a larger pull. To be
more precise about the pulls and pushes you are applying, you need a device to measure
forces accurately. The electronic force probe is designed to do this.
Activity 1-2: Measuring Forces With a Force Probe
In this activity you will explore the capability of an electronic force probe as a force measuring
device.
1. Plug the force probe into the computer interface. Display force vs. time axes by
opening the experiment file called Measuring Force (L03A1-2a).
If the sensitivity of your force probe can be adjusted, choose the setting appropriate to the
measurements in this activity (about 0 to 10 N or more).
3
