Companion to the reading passage The Physics of the Fist: Force, Impulse, and the Evolution of the Boxing Glove. Answer each question, then click Check. Multiple-choice and number questions grade themselves; for written answers, compare yours with the model answer and checklist, then score yourself honestly.
Boxing was fought bare-knuckle in England until the Queensberry Rules of 1867 made padded gloves mandatory. Today, engineers test gloves with a mechanical arm. The arm swings a rigid model fist straight into a padded crash-test dummy head that is mounted on a force sensor. In each trial the model fist is moving horizontally at the same speed when it strikes the head, and it comes to a complete stop during the collision.
Diagram 1: A dot represents the model fist at the instant it touches the dummy head. The fist is moving to the right, toward the head. An arrow pointing to the right, 2 centimeters long, has already been drawn from the dot. It represents the force of the fist on the head during the collision.
Diagram 1
1. Using the 2-centimeter arrow in Diagram 1 as a scale, choose the direction of the arrow that represents the force of the head on the fist during the collision, and enter the length of that arrow (right is the direction the fist is moving).
The engineers ran three trials. In trial A the model fist was bare. In trials B and C the same model fist wore a glove; glove C was thicker and heavier than glove B. The mass in Table 1 is the total mass of the moving fist and glove. The force sensor recorded how long the fist was in contact with the head before it stopped.
Table 1: Impact Trials
| Trial | Fist Condition | Total Moving Mass (kg) | Speed Just Before Impact (m/s) | Contact Time (s) |
|---|---|---|---|---|
| A | Bare fist | 0.60 | 8.0 | 0.0040 |
| B | Thin glove | 0.80 | 8.0 | 0.016 |
| C | Thick glove | 1.00 | 8.0 | 0.025 |
Data are representative values for practice.
2. Which mathematical representation can be used to determine the magnitude of the average force on the bare fist in trial A?
3. An engineer makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
Training gloves are usually thicker and heavier than competition gloves. To see the effect of the extra padding and mass, the engineers compared trial C with trial B. In both trials, the impulse the head exerts on the fist is the impulse needed to bring the moving fist and glove to a stop.
4. Which row correctly compares trial C with trial B? (Magnitude of change in momentum of the fist and glove / Average force on the head)
5. Substitute numerical values into a mathematical representation that can be used to determine the magnitude of the impulse that the head exerts on the fist and glove in trial C. Then calculate the impulse.
The human hand contains 27 small bones, while the skull is a thick, rigid dome. A bare-knuckle fighter who punches the head at full speed risks breaking the bones of the hand, so bare-knuckle fighters tend to throw fewer full-force punches to the head. Padding protects the hand, so gloved boxers can throw many full-force punches to the head over a fight that may last up to 12 rounds. Physicians are concerned that many repeated head impacts over a career can cause long-term brain injury, even when each single impact is softened by padding.
6. A glove company plans to make its competition glove thicker and heavier, like glove C. Using evidence from Table 1, identify one benefit and one drawback of this design change for the safety of the person being hit.