Download MS Word

HPP Activity A29.v1
This is a lot of work
You can now understand and calculate the motion of any object undergoing constant
acceleration. You can determine how far, how fast, starting location, starting velocity, and the
acceleration of any object. You've jumped into the air and measured your position and velocity as
a function of time. You have also related accelerated motion to applied forces, drawn free-body
diagrams, and constructed equations of motion using those free-body diagrams and Newton's
laws of motion. You have related these ideas to various physical activities. What gives you the
ability to jump, or do any other physical activities in the first place? It is one of the most
essential components of the universe and is critical to all people. We are talking about energy.
Exploration
Let’s get to work!
GE 1.
1. Write a definition for Energy.
2. How do you get energy in order to do you physical activities?
3. What unit do you use to measure that energy?
4. Define the unit for measuring food energy. If you don’t know it from
chemistry, go look it up.
5. Can you relate this energy unit to any other units for energy measurement?
6. So how much physical exertion does it take to “burn off” that energy you
took in at lunch? Let’s be specific, how many steps do you think you would
have to run up to “burn off” lunch?
7. Is your estimate a guess or is it based on a calculation? If so, show the
calculation.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and DUE #00-88780
HPP Activity A29.v1
2
In order to answer this question more definitively, we better do a little exploring first. Let’s
investigate the factors that affect the amount effort you exert during an activity.
GE 2.
1. Begin by placing the physics cart on the floor and have a group member sit
on the cart. Attach the spring scale on to the cart and make sure the friction
plate is not down. Pull on the spring scale so that the cart moves at a constant
velocity for one meter. Record the spring scale reading when the cart is
moving at a constant velocity. Repeat with the friction plate down so that you
notice a moderate amount of friction, and again with a considerable amount of
friction. Record your results.
Amount of friction
Small
Medium
large
F [N]
2. Suppose there was truly no friction at all on the cart. What force would be
required to keep the cart moving at constant velocity?
3. Determine which trial required the most effort and support your
conclusion with data from your investigation.
4. Now do one more trial. Keep everything the same as trial three, but
increase the distance to 4 meters.
5. How does increasing to 4 meters affect the amount of effort you exerted?
Invention
GE 3.
1. From your explorations, what are the two main factors that affected the
effort required to pull the cart?
2. What kind of relationship exists between each of these factors and the
effort required?
Activity Guide
 2010 The Humanized Physics Project
HPP Activity A29.v1
3
3. If you had to pull this cart around all day, you might consider this some
pretty tough work. In fact, this is Work, even by the definition in the physics
world. Using what you now know about Work, come up with a formula that
solves for Work. Check with your instructor.
4. Now substitute SI base units of measure in the formula to come up with
the unit for Work. What derived SI unit is this equal to? If you don’t know
you can ask the instructor.
Application
To the stairmaster!
GE 4.
1. Now back to the question of how much Work you have to do to “burn off”
lunch. Let’s say you had a Big Mac for lunch (about 700 Calories). We want
to determine how many steps you must run up to burn this meal off. Start
with moving up 1 meter. How much work must you do to move vertically
upwards one meter at constant velocity?
2. How many steps must you go up to burn off lunch?
3. How much energy does an average person take in everyday? Based on
your results from the Big Mac calculation, do you think you do enough
physical activity to work off all the energy you take in everyday?
4. What are some other important functions your body uses energy for?
Which one do you think requires the most energy? Defend your answer.
Exploration
You have investigated how force and distance are related to the amount of Work you do. How
does changing the angle the force is applied at affect the Work?
Activity Guide
 2010 The Humanized Physics Project
HPP Activity A29.v1
4
GE 5.
1. Use the same cart set up as in the earlier exploration. Set the friction plate
so there is some light friction on the cart. Attach the spring scale to the cart
making sure the scale is always parallel to the floor while you are pulling the
cart. Using a protractor to measure the angle, find the force needed to pull the
cart at a constant velocity when the spring scale is at angles of 0, 30, 60, and
90 degrees. Record your data.

Fp [N]
2. What happens to the force you must apply in order to achieve constant
velocity as the angle is increased?
Invention
GE 6.
1. Using the forces and angles from the exploration, determine the
component of the pulling force parallel to the direction of motion. Make sure
you make a sketch of the forces on the cart and write the formula that you are
using.
Top View of Cart
2. How do the parallel components of pulling force for each trial compare?

Activity Guide
 2010 The Humanized Physics Project
Component of Fp [N]
HPP Activity A29.v1
5
4. How much work does the perpendicular component of pulling force do on
the cart? Think about the trial for  = 90.
5. How much work does the parallel component of pulling force do on the
cart for each trial?
6. Write the formula for finding work when the pulling force is at angle 
with respect to the direction of travel. Check with instructor.
Application
GE 7.
1. Write the work done on the cart in terms of the friction force on the cart.
2. Using the results from above, write the work in terms of the pulling force,
at an arbitrary angle.
3. Try to find an equation that relates the ratio Ff/Fp to the angle.
4. Graph your experimental values of Ff/Fp versus angle and theoretical
values.
5. How does the experimental curve compare to the theoretical curve?
Application
GE 8.
1. Suppose you are pulling the cart at an angle of 30 degrees in the vertical
direction with a force of 40 [N]. How much work is done on the cart after
pulling it 4 meters?
Activity Guide
 2010 The Humanized Physics Project
HPP Activity A29.v1
Activity Guide
 2010 The Humanized Physics Project
6