Instructor Outline:
Work and Energy
UM Physics Demo Lab 07/2013
Lab length: 70 minutes
Lab objectives: To teach the definitions of work and energy, kinetic energy,
gravitational potential energy, the Work-Energy Theorem, to demonstrate nonconservative work due to friction and to demonstrate energy conservation for cars
rolling down ramps.
Materials
8 calculators
Dedicated Components
8 Pitsco PC Sportster cars
8 Hot Wheels cars with aluminum
photo gate flags
8 sets of ½ inch x 2” steel hex bolts
with nuts
8 sets of 8 ½ inch cut steel washers
8 10’ steel wall stud ramps
8 Homer bucket ramp supports
8 Guide Wire Assemblies
8 spring scales– Ohaus 2000g/20N
8 clear plastic rulers
8 meter sticks
8 2” long thin rubber bands or thread
loops
8 digital gram scales
8 digital stop watches
Shared/Consumable Components:
Additional rubber bands
8’ ramp for speed trap
4 Homer Buckets, 2 with lids for ramp
support, one for car catcher, one for
scale stand.
Pulley, ring stand and 50 g digital
scale for measuring gravitational force
down ramp
Clear package tape
Scissors
Data acquisition system for Pitsco
cars: ring stand photo gate support,
laptop PC running Logger Pro “speed
trap” application and MS Excel
**Demonstrations:
1M30.u1 Downhill Duck
1M40.20 - Loop the Loop
Introduction: 5 minutes-Lecture
The definitions of work and energy are introduced.
Exploration stage: 10 minutes-Group lab work
Students explore the work done by gravity on Pitsco cars rolling on ramps by measuring
the force due to gravity along the ramp and multiplying by the distance down the ramp.
Analysis Stage: 10 minutes-Lecture
The results of the first ramp experiments are reviewed. Next definitions are given for
kinetic energy and gravitational potential energy. Finally, the Work-Energy Theorem is
stated.
Exploration Stage: 15 minutes-Group lab work
Students perform additional experiments to make quantitative estimates of the kinetic
and gravitational potential energy for cars rolling down ramps.
Analysis Stage: 5 minutes-Lecture
Property of LS&A Physics Department Demonstration Lab
Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109
The concept of gravity as a conservative force is introduced, the Work-Energy Theorem
is further discussed and energy conservation is motivated as an accounting “balance
sheet”.
Application Stage: 15 minutes-Class group activity
Each group is assigned a Hot Wheels car and then measures the component of their
car’s weight down the demonstration ramp. Each group then measures the car’s final
speed at the bottom of a ramp with the same “speed trap” apparatus as used for the jet
car experiment (Newton’s Laws of Motion lab). The data are entered into Excel in realtime for all the class to observe.
Analysis and Summary Stage: 10 minutes-Lecture/Class Discussion
The results of the quantitative energy conservation experiment are discussed, energy
lost to friction and the friction force are estimated. A final review of work, energy and
the Work-Energy Theorem is presented. The special status of gravity as a conservative
force for which work can be calculated as the change in a potential energy function is
stressed.
Concepts developed:
1. Definition of mechanical work
2. Definition of kinetic energy.
3. Definition of gravitational potential energy.
4. Gravity as a conservative force and the connection to gravitational potential
energy.
5. Work-Energy theorem.
6. Energy conservation.
7. Nonconservative work as evidenced by energy lost to friction.
Property of LS&A Physics Department Demonstration Lab
Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109