power

ANATOMICAL KINESIOLOGY LABORATORY EXPERIENCE

HUMAN WORK AND POWER: LABORATORY ASSIGNMENT AND STUDY WORKSHEET.
PROFESSOR: DR. LEO D’ACQUISTO

Introduction:

The following assignment is designed to provide you with an understanding of work and power. Please work through the laboratory assignment; however, it does not need to be turned in for a grade. Get together with some of your classmates or several of your friends and determine human work and power as outlined below. Have fun!

Purpose: The purpose of the following laboratory assignment will be to calculate human work and power using a Stair Run Test. In addition, the relationship among human work, body weight power and stair run time will be examined.

Terminology

A. Work is defined as the application of force through a given distance. Your textbook defines work as .."the productof the amount of force expended and the distance through which the force succeeds in overcoming a resistance it acts upon.”

Work = Force x Distance
(W) (F) (D)

For example: if you move a given weight (3 kg) vertically 1 meter, you have performed 3 kg-meters of work (3kg x 1 meter).

B. Power is work expressed per unit time, or simply the rate of doing work.

Power = Force x Distance
Time

For example, if 3 kg were moved vertically 1 meter in 2 seconds, the power generated would be,

Power = 3 kg x 1 meter
2 seconds

= 1.5 kg-meter per second

Power is therefore a combination of strength and speed. Make note that power makes reference to the rate of doing work.

C. Energy Energy is defined as the capacity to do work. Both energy and work have the same unit of measure (i.e., kg-m, or joules). A body possesses energy when it can perform work. Therefore, the energy possessed by the body is calculated as the amount of work accomplished. The following are two classifications of mechanical energy:

1. Potential energy refers to the capacity of a body or object for accomplishing work based on its position or configuration. For example, a diver on a platform, a bent bow, or a compressed spring all have the ability to produce work or potential energy. Equation for potential energy,

Potential energy = mgh

Where, m=mass; g=acceleration due to gravity, h=height between objects center of gravity (i.e., diver) and the surface upon which the object will land (i.e., water).

2. Kinetic energy refers to a body’s energy due to its motion. The faster a body is moving, the greater its kinetic energy. When an object stops moving, its kinetic energy is dissipated. Why?, because kinetic energy is directly related to velocity. The formula for kinetic energy is the following:

Kinetic energy= ½ mv2

Where, m=mass of object, and v=velocity of the object. If velocity is zero, kinetic energy is also zero. Recall that energy can neither be created nor destroyed (Law of Thermodynamics), and, that energy is the capacity to do work. Therefore, the amount of work accomplished is equal to the kinetic energy acquired by the object, in equation form the latter would be represented as follows:

Force x distance = ½ mv2
(Work) (Kinetic energy)

The above equation implies that it is important to “give” when receiving an object with kinetic energy (moving object). For example, when attempting to catch a fast moving baseball, meaning that the ball has a high kinetic energy, it is best to increase the amount of stopping distance. By “giving” or increasing the stopping distance, you have decreased the amount of stopping force of the ball. In other words, by increasing stopping distance by giving, you are increasing the amount of time in which the kinetic energy of the fast moving ball is dissipated, or reduced to zero. Therefore, you have lessen the magnitude of impact and also the likelihood of becoming injured.

Example of a diver to illustrate that energy is frequently transformed from kinetic energy to potential energy or potential energy to kinetic energy.

On the diving platform, a diver has potential energy but no kinetic energy. When the diver jumps, the increase in kinetic energy is proportional to the decrease in potential energy, providing no eneryg is lost as heat or sound. The latter suggests that the total energy of the event is remaining constant. In addition the latter example suggests that the kinetic energy at the bottom of the dive equals the potential energy while standing on the board.

Example of a gymnast swinging on the flying rings to illustrate that energy is frequently transformed from kinetic energy to potential energy or potential energy to kinetic energy.

In a stationary and elongated position at the top of the flying rings, the gymnast has potential energy for doing work. As the gymnast falls, or swings downward, kinetic energy increases and becomes complete at the bottom of the swing. At the bottom, speed is greatest and potential energy is zero. On the upswing, kinetic energy is lost and potential energy is gained. Potential energy is greatest at the top of the flying rings. Kinetic energy is lost on the upswing because the gymnast begins to slow down as potential energy is gained. In essence the gymnast acts as a pendulum. At some point the gymnast would come to a stop or rest because some energy is converted to heat due to friction between the gymnasts hands and rings.

Procedure:

Equipment: Good athletic shoes for running, stop watch, notepad for recording data and great enthusiasm!! It would be best to have 10 to 12 participants.

I. Stair Run Test
The test for power will be a Stair Run Test. Subjects will be tested on a flight of stairs with a 7-8 inch rise per step, with at least an eight to ten foot approach. A stop watch will be used for timing. The subject is to go up the stairs one step at a time. The vertical distance covered is 2.0 meters. Each subject will get 2 or 3 trials. The fastest time will represent the stair run time. The timer starts the stop watch when the foot makes contact with the first step and stops the stop watch when the foot makes contact with the top step (instructor will illustrate). Be carefull not to trip. **It is important that you give your best effort. Record your best time.

Use the following formula to compute work:

Work = Body weight (kg) x Distance (meters)

work units, kilogram-meter

Use the following formula to compute power:

Power = Body weight (kg) x Distance (meters)
Time (seconds)

power units, kilogram-meter per second

Subjects body weight, convert lbs to kg, lbs/2.2 = kg
Vertical distance, 2.0 meters

II. Sprint performance (50 meters) (Will not be performed in this laboratory experience)

Perform a 50 meter sprint on the track following a 5 to 10 minute rest from the stair run test. **It is important that you give your best effort. Perform two trials with a 3 to 5 minute rest. Record your best time. Express your sprint performance time as velocity (meters per seconds).

Results: What did you find? All raw data should be presented in table and graphical format. Please label your tables and graphs. Record individual data for work, power, and stair run time. In addition, plot the relationship between work (Y axis) vs body weight, power (Y axis) vs. work, power (Y axis) vs body weight, and power (Y axis) vs stair run time.

Discussion and Study questions.
Discuss the following questions in a study group setting. Prepare by having written answers to the questions.

1. What is the difference between work and power?

2. Discuss the relationship between work vs body weight, power vs. work, power vs body weight, and power vs stair run time.

• Which subjects did the most work. Why?
• Does the amount of work accomplish predict power?
• Is body weight a good predictor of power?
• Is stair run time a good predictor of power?

3. What is the discriminating factor in athletic performance? Is it the amount of work an individual performs or power output? Explain.