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Putting It All Together: Energy and Motion

Getting Started

The previous lessons and activities in this unit provided examples that demonstrate the physical science concepts of mechanical energy, work and power, momentum and collisions, and friction and drag, while water wheels were used as a demonstration of work and power, if you look deeper into a water wheel system, you will see aspects of mechanical energy, momentum, and friction as well. Water turns the wheel by going from a high potential energy to kinetic energy. Also, if no load existed on the waterwheel and the water supply ran out, the wheel would keep turning, showing signs of momentum. However, friction would eventually bring the wheel to a stop.

In real-world physical systems, these energy of motion concepts are commonly interconnected with each other. Much of our everyday lives and safety depend on engineers designing vehicles and structures with a firm understanding of these concepts and their interaction. Imagine how these concepts interact in the use of skateboards, scooters, roller coasters, trains, cars, planes, trucks, bicycles, elevators, etc. In this lesson, we put all of these concepts together to understand how they work collectively in a hands-on, inclined ramp associated activity Energy In Collisions and Rolling Ramp Review.

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Engineering Connection

Light rail trains are a modern form of public transportation powered by overhead electrical lines that travel along dedicated pathway of steel rails. To design these trains to be quiet, efficient and safe, engineers consider all of the energy of motion concepts: the work required to convert the mechanical energy when the train goes from a stopped position to forward/backward motion, how much momentum the train acquires between stations, and the power required to overcome the friction between the train's wheels and the effects of drag.

Picture yourself atop a big hill with a scooter. Do you know how much potential energy you have? How fast will you be going when you reach the bottom? How much momentum will you have at the bottom? If you press hard on your brakes and slide to a stop, how much work will friction have done? Today's activity models this scenario and helps you answer these questions

Energy in Collisions Activity: Materials

• yardstick (for the activity setup)
• metric ruler (for measuring distance)
• 4 dowel rods, 3 ft long, ¼-inch thick
• golf ball (or similar sized ball)
• plastic or Styrofoam cup (must be lightweight, not heavy)
• scale (to weigh the golf ball)
• tape
• paper towels or tissues
• Ramp and Review Worksheet

Think of situations that involve a combination of mechanical energy, momentum and collisions, work and power, and friction.

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Energy in Collisions Activity: Procedure

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Activity set-up. The height, h, is the vertical distance from the ground to the top of the angled yardstick. The distance, d, is the horizontal distance from the bottom of the ramp to the point where the cup with the ball comes to a rest.

1. Tape a dowel rod to each side of a yardstick, approximately 1-inch apart from each other. This serves as a track for the golf ball to roll down.
2. Prop the yardstick against a wall or desk to create a slope for the ball to roll down.
3. Place a small amount of crushed paper towels or tissues inside the cup to absorb the impact of the ball and keep the ball in the cup.
4. Place the cup at the end of the yardstick ramp to catch the ball at the end of the incline.
5. Tape the other two dowel rods a few inches apart to create a track for the cup to slide along.
6. On the worksheet, complete questions 1 and 2 (measure the height of yardstick and weight of golf ball).
7. Place the ball at the top of the ramp and let it go.
8. Measure the distance the cup travels at the end of the ramp and record that for question 3 on the worksheet.
9. Complete the calculations on the worksheet.

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Review: Tell Someone What you Learned Today

1. What would happen if a heavier glass cup was used instead of a lightweight cup for this activity?
2. How did the friction, momentum, kinetic and potential energy, and work and power all come together to make the cup move?
3. How does this relate to activities you do every day? Can you give examples of things that relate to friction, momentum, kinetic and potential energy, and work and power? teachengineering.org