2.1 Energy: Speed and Mass Study Guide

CHAPTER 2

Strand 2: Storing and Transferring Energy

Chapter Outline

2.1 ENERGY: SPEED AND MASS (8.2.1)

2.2 POTENTIAL ENERGY (8.2.2)

2.3 ENERGY TRANSFER (8.2.3)

2.4 WAVES (8.2.4)

2.5 WAVES AND MEDIUMS (8.2.5)

2.6 ANALOG AND DIGITAL SIGNALS (8.2.6)

Objects can store and transfer energy within systems. Energy can be transferred between objects, which involves changes in the object’s energy. There is a direct relationship between an object’s energy, mass, and speed. Energy can travel in waves and may be harnessed to transmit information.

2.1 Energy Speed and Mass (8.2.1)

Explore this Phenomenon

These two trucks run into an empty building. One truck causes more damage to the building than the other.

1. What observations can you make about the trucks?
2. What questions can you ask to determine why one truck causes more damage than the other?
3. How would you explain why one truck causes more damage than the other?

8.2.1 Energy: Speed and Mass

Use computational thinking to analyze data about the relationship between the mass and speed of objects to the relative amount of kinetic energy of the objects. Emphasis should be on the quantity of mass and relative speed to the observable effects of the kinetic energy. Examples could include a full cart vs. an empty cart or rolling spheres with different masses down a ramp to measure the effects on stationary masses. Calculations of kinetic and potential energy will be learned at the high school level. (PS3.A, PS3.C)

In this section, focus on scale, proportion, and quantity and cause and effect. Proportional relationships (e.g. speed as the ratio of distance traveled to time taken) coupled with quantity measurements (mass) provide information about the magnitude of an object’s kinetic energy. Cause and effect relationships may be used to predict relative amounts of kinetic energy.

Kinetic Energy

What do these four photos have in common?

Energy exists in many different forms, but the one you should be very familiar with is kinetic energy. Kinetic energy is often thought of as the energy of motion because it is used to describe matter that is moving. The spinning saw blade, flying bee, racing motorcycle, and the flowing water in the photos are moving; therefore, the common factor in all the pictures is kinetic energy.

What is Energy?

• the ability to due "work" ...the ability to move something against a force

Kinetic Energy: energy of motion

• describes objects that are moving
• depends on two factors: speed and mass

The effects of mass on Kinetic Energy:

• The larger the mass, the more kinetic energy an object has

The effects of speed on Kinetic Energy:

• The greater the speed, the more kinetic energy an object has

K = 1/2mv²

(Kinetic Energy = 1/2 x mass x velocity x velocity)

So:

• Kinetic Energy increases as much as mass increases

• Kinetic Energy increase faster than speed increases

Factors Affecting Kinetic Energy

An object’s kinetic energy depends on two things, its mass and speed. The greater the mass, the more kinetic energy the object has. Speed, which is how fast an object is moving (meters/second), also influences kinetic energy. The greater the speed, the greater the kinetic energy. Think back to the questions you were asked at the beginning of this section about the truck pictures. Which moving truck would have more kinetic energy due to its mass, the large dump truck or the smaller truck? How would speed affect the truck’s kinetic energy?

Kinetic energy can be calculated by using the formula KE = ½(mv 2 ). This formula is read as kinetic energy equals one half of the mass times square of the speed.

If we take a closer look at the formula you will be able to see why changes in speed have more of an impact on kinetic energy than changes in mass. Use the space below to explain this phenomenon in your own words.

Putting It Together

1. Explain how your understanding of kinetic energy has changed.
2. Think of another phenomenon that applies to how mass & speed affect kinetic energy.
3. Explain what the difference in kinetic energy will be for these two trucks based on what you have learned in this section.