Physics-Energy Forms and Transformationname ______

Physics-Energy Forms and TransformationName ______

Refer to Pages 135-143

1. See Table 1 on page 143. Which activity uses the most energy? The least?

1. Consider everything that you do in a day and calculate the number of hours you do them. Then estimate how many Calories you used during in that day.

1. See page 142. Read the Human Body—Balancing the Energy Equation: Why are our bodies warm? Where did the energy come from?

1. Describe the energy transfers in Figure 5.

1. How would using a light bulb with a greater Wattage affect the energy flow?

1. See Figure 6. Describe the energy transformations that occur to cause a car to move.

1. See Figure 7. What happens to the mechanical energy of the apple as it falls from the tree.

1. See Figure 8. Explain what causes the baseball to increase in GPE, to decrease in GPE, to increase in KE and to decrease in KE.

1. What pattern do you observe with the speed and height of the batted ball as it is related to energy.

1. See Figure 9. Describe the energy transformations associated with a pendulum or a person on a swing.

1. See Figure 10. What does this figure illustrate about the law of conservation of energy?

1. Read The Effect of Friction on page 140. How does friction influence the mechanical energy of any moving object?

Physics-Energy Forms and TransformationName ______

Refer to Pages 135-143

1. See Table 1 on page 143. Which activity uses the most energy? The least?

Running uses the most energy per hour, sitting uses the least.

1. Consider everything that you do in a day and calculate the number of hours you do them. Then estimate how many Calories you used during in that day.

1. See page 142. Read the Human Body—Balancing the Energy Equation: Why are our bodies warm? Where did the energy come from?

Our bodies are warm because of our life processes. The food we eat stores chemical potential energy which is released when our food is digested. This transfers energy from the food into our bodies, where much of the energy is converted into heat or thermal energy. This continuous energy transfer process occurs every second of our lives.

1. Describe the energy transfers in Figure 5.

Electrical energy from the power plant is transferred to light energy and thermal energy at the filament of the light bulb which is emitted into the room

1. How would using a light bulb with a greater Wattage affect the energy flow?

A light bulb, say, that uses 60 W of power requires 60 joules of electrical energy per second to operate at full capacity. A light bulb that uses 100 W of power would require an additional 40 joules of electrical energy per second to function. So more Wattage means more energy is required per second.

1. See Figure 6. Describe the energy transformations that occur to cause a car to move.

Cars require fuel to operate. The internal combustion engine of a gasoline-powered car burns gasoline, which releases the chemical potential energy stored in the bonds of the compounds that make up this fuel. The energy is released as thermal energy, and the expanding gases from combustion do work on the piston in the cylinder, causing it to move, which leads to the movement of the wheels.

So chemical PE is transferred to thermal energy which is transferred to KE as the car moves.

1. See Figure 7. What happens to the mechanical energy of the apple as it falls from the tree.

The mechanical energy of the apple is equal to the KE and the GPE of the apple. Since the apple is at rest, the total mechanical energy of the apple is equal to the GPE. As the apple falls, the GPE of the apple is transferred to KE, but the total mechanical energy of the apple remains the same illustrating the law of conservation of energy.

1. See Figure 8. Explain what causes the baseball to increase in GPE, to decrease in GPE, to increase in KE and to decrease in KE.

The batted baseball increases in GPE because it increases in height and decreases in GPE because it decreases in height. The KE of the baseball decreases as the ball rises, but increases as the ball falls toward the field.

1. What pattern do you observe with the speed and height of the batted ball as it is related to energy.

Increased height causes an increase in GPE but a decrease in KE. Decreasing height causes a decrease in GPE but an increase in KE. It is an inverse pattern.

1. See Figure 9. Describe the energy transformations associated with a pendulum or a person on a swing.

As the pendulum swings downward, it gains KE as its GPE decreases, which increases its speed. As the pendulum swings upwards, the pendulum transfers KE to GPE as the pendulum’s speed decreases and its height increases.

1. See Figure 10. What does this figure illustrate about the law of conservation of energy?

Energy in = Energy out. The amount of electrical energy in used to power the hair dryer is equal to the amount of energy transferred out to thermal energy plus kinetic energy of the motor and fan plus the sound energy.

1. Read The Effect of Friction on page 140. How does friction influence the mechanical energy of any moving object?

Friction (and air resistance) cause some of the mechanical energy of the moving object to change to thermal energy. This reduces the speed of the object, but increases the temperature of the surroundings. So the original KE is not destroyed, it just is transformed into thermal energy.