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Force versus
distance graph
Objectives
- Investigate examples of kinetic and potential energy and their transformations.
- Calculate work from the area under the force vs. distance graph.
- Relate the net work done on an object to its change in kinetic energy.
- Demonstrate the use of course apparatus and equipment, including slotted or hooked masses, spring scales, meter sticks, graph paper, graphing technology, and data acquisition probes. An elastic band is stretched 40 cm and used to accelerate a cart.
Assessment
- How much work is done on the cart when the band is released? 2. BEFORE the elastic band does work on the system, what type of energy does the system have, and how much? 3. AFTER the elastic band does work on the system, what type of energy does the system have, and how much?
Assessment
An elastic band is stretched 40 cm and used to accelerate a cart.
Physics terms
- force
- work
- force vs. distance graph
Equations
Work done by a constant force: Area of a rectangle: Area of a triangle:
Reviewing the concept
The work done by a force equals the force times the distance moved in the direction of the force.
Reviewing the concept
A constant force of 4 N acts on an object in the direction of its motion. If the object moves 2 meters, how much work is done?
Reviewing the concept
A constant force of 4 N acts on an object in the direction of its motion. If the object moves 2 meters, how much work is done? A graph of force vs. distance for this event is shown. A constant force of 4 N acts on an object in the direction of its motion. The object moves 2 meters.
Reading the graph
The work done equals the area of the shaded rectangle.
Area under the graph
- If the force is constant, this area is a rectangle.
- But what if the force is not constant?
Area under the graph
The work done equals the area under the force vs. distance graph.
a. How does the work done by the elastic band compare with the Ek of the ErgoBot? Why? b. What are the independent, dependent, and controlled variables?
Investigation
Questions for Part 1 Gather your materials. Select a hanging mass that allows for a brisk but controlled acceleration.
Investigation
Part 2: Gravitational force
- Release the suspended mass and capture the motion data on the computer.
- For at least 5 points on the motion graph, determine the distance traveled and the acceleration. Part 2: Gravitational force
Investigation
- Calculate the net force at each distance by applying Newton’s second law: Fnet = ma. Part 2: Gravitational force
Investigation
- Plot a graph of force vs. distance for the ErgoBot.
a. Use the motion graphs to determine vmax at the end of the
accelerated motion. What was the maximum Ek? b. Calculate the total work done on the ErgoBot from the area under the graph of force vs. distance. c. How does the total work done on the ErgoBot compare with its maximum kinetic energy?
Investigation
Questions for Part 2 An elastic band is stretched 40 cm and used to accelerate a cart.
Assessment
- How much work is done on the cart when the band is released?
Assessment
- How much work is done on the cart when the band is released? An elastic band is stretched 40 cm and used to accelerate a cart.
Assessment
- BEFORE the elastic band does work on the system, what type of energy does the system have, and how much?
- AFTER the elastic band does work on the system, what type of energy does the system have, and how much? An elastic band is stretched 40 cm and used to accelerate a cart.
Assessment
- BEFORE the elastic band does work on the system, what type of energy does the system have, and how much?
- AFTER the elastic band does work on the system, what type of energy does the system have, and how much? elastic potential energy = 4 J An elastic band is stretched 40 cm and used to accelerate a cart.
Assessment
- BEFORE the elastic band does work on the system, what type of energy does the system have, and how much?
- AFTER the elastic band does work on the system, what type of energy does the system have, and how much? kinetic energy = 4 J elastic potential energy = 4 J An elastic band is stretched 40 cm and used to accelerate a cart.
