{Physics 20/30; Core Unit II: Mechanical Energy (A) Work (C) Kinetic Energy}
Deadfall Trap Physics Lab
Using Conservation of Energy to determine Average Impact Force
Deadfall traps have been used by First Nations of North America for generations as a method of obtaining food and
other resources from wildlife. The trap consists of 3 sticks notched together in a particular way to form the trigger
apparatus, and a heavy log or board which falls on the animal. Oral history suggests that as a rule of thumb, the
weight of the board should be three times the weight of the animal to be caught. Conservation of energy and the
formula for work can be used to determine the force exerted by the board when it falls.
Purpose:
To explore the relationship between
 mass of the board and the average impact force of the deadfall trap
 height of the board and the average impact force of the deadfall trap
Related Media:


Video, ‘Deadfall Trap Physics’ by Barry Linklater
Teacher Resources: Energy Lesson Plan.pdf; Lab Assessment Worksheet.pdf (and answer key)
Materials (needed for each group of 2-3 students)
 Deadfall trap trigger system (3 small sticks with particular notches)
 3 Boards of the same dimensions but varying mass (suggested: Styrofoam, cedar or pine, maple
or oak)
 Scale
 Play-dough
 Meter stick
 string
Set Up:
This hands-on activity has been developed by for the Saskatchewan Cradleboard Initiative by students Kyle Harms, and Heidi Neufeld; with the guidance of
Engineering Professor Dr. Sean Maw. This document is licensed to the Creative Commons and may be distributed freely with attribution for any and all noncommercial educational purposes
{Physics 20/30; Core Unit II: Mechanical Energy (A) Work (C) Kinetic Energy}
Procedure
Part A: Mass and Average Impact Force
1. Find the mass of each of the three boards and record these values in the data table.
2. Find the center of gravity of each of the boards and mark it with a dot and a line across the short
length of the board (perpendicular to the long edge of the board).
3. Tie the string around the free end of the bait stick.
4. Set up the deadfall trap as shown above using the Styrofoam board.
5. Measure the height of the center of gravity of the board and record it in the data table.
6. Shape a piece of play-dough into a cylinder around 4 cm in diameter and 10 cm in length.
Measure the exact diameter and height of your play-dough and record it in the data table.
7. Place the cylindrical-shaped play-dough beneath the board around the end of the bait stick.
8. Trip the bait stick and let the board fall on the play dough.
9. Measure the height of the play-dough again, and record it in the data table.
10. Repeat steps 3-9 using the cedar wood board. Use the same size play-dough cylinder.
11. Repeat steps 3-9 using the maple wood board. Use the same size play-dough cylinder.
Part B: Height and Average Impact Force
1. Set up the deadfall trap as shown in the picture above using the maple wood board.
2. Measure the height of the center of gravity of the board and record it in the data table.
3. Shape a piece of play-dough into a cylinder the same size as used in part A.
4. Place the cylindrical-shaped play-dough beneath the board at the end of the bait stick.
5. Trip the bait stick and let the board fall on the play dough.
6. Measure the height of the play-dough again, and record it in the data table.
7. Repeat steps 1-6 but this time increase the center of gravity of the board by increasing the angle
of the board with the table. Use the same size play-dough cylinder.
8. Put away all materials.
Type of board
Mass of the
board
Height of
board’s center
of gravity
Part 1
Styrofoam
Constant:
Cedar wood
Constant:
Maple wood
Constant:
Play-dough
diameter
(constant)
Play-dough
initial height
(constant)
Playdough
final
height
Change in
height
Δ𝑑
Kinetic
energy
Impact
Force
KE
F
Part 2
Maple wood
Maple wood
Results and Calculations
This hands-on activity has been developed by for the Saskatchewan Cradleboard Initiative by students Kyle Harms, and Heidi Neufeld; with the guidance of
Engineering Professor Dr. Sean Maw. This document is licensed to the Creative Commons and may be distributed freely with attribution for any and all noncommercial educational purposes
{Physics 20/30; Core Unit II: Mechanical Energy (A) Work (C) Kinetic Energy}
Show one sample calculation for each step on a separate piece of paper to be handed in.
1. Calculate the change in height of the play-dough in each trial (note-this value should be negative
since the play-dough ended up shorter). Record these values in the data table.
2. Consider: How did Δ𝑑 change throughout the different trials?
3. Using conservation of energy, calculate the kinetic energy of the board for each of the trials.
Record these values in the data table.
1
(Conservation of energy states that𝑃𝐸 = 𝑚𝑔ℎ → 𝐾𝐸 = 2 𝑚𝑣 2)
4. Consider: How did KE change throughout the different trials?
5. Use the two formulas for work to find the impact force of the board on the play-dough.
(Work formulas are 𝑊 = 𝐹Δ𝑑 and𝑊 = Δ𝐾𝐸)
6. Consider: How did the impact force change throughout the different trials?
7. Mathematically, should the velocity of the falling board change when mass increases? Why? If
you observed something different than what the formula predicts, why might this happen?
Conclusion

Write a detailed but concise summary of your results. Include sources of error and suggestions
for future experiments/inquiry.
Additional Points for Discussion:
Center of gravity – why can we treat the entire board as a point mass?
Answer: Split up the board into slices. Consider the height of each piece and the mass of each piece.
Find the KE of each, and add them all up. It will be the same as the KE for the board as a point mass.
Velocity is independent of mass.
When the mass falls, its velocity is only dependent on the height from which it falls.
1
𝑃𝐸 = 𝑚𝑔ℎ → 𝐾𝐸 = 𝑚𝑣 2
2
Find the velocity using conservation of energy. Does it change? (No).
This hands-on activity has been developed by for the Saskatchewan Cradleboard Initiative by students Kyle Harms, and Heidi Neufeld; with the guidance of
Engineering Professor Dr. Sean Maw. This document is licensed to the Creative Commons and may be distributed freely with attribution for any and all noncommercial educational purposes