Warm up

Draw an energy chain of a soccer player kicking a soccer ball into a goal. Start with a soccer player who has CPE from food they ate that morning and ending with a ball rolling into the goal.

WORK The Transfer of Energy

How does the previous investigation help us to understand how forces transfer energy?

W=fxd

Safer Barriers

• http://www.youtube.com/watch?v=ALHW4zq KB6E

Forces That Transfer Energy

Making Crash Barriers

Pre-Investigation Questions

• Question #1: What form of energy is present when the car is sitting at the top of the ramp? How do you know this?

• Question #2: What will happen to the energy of the car as it moves down the ramp? What evidence could you collect to justify your answer?

• Question #3: When the car strikes the barrier what will happen to the energy of the car? How do you know this?

• Question #4: Let’s assume we release the car from rest at the top of your ramp. What can you do to be sure that the car strikes your barrier with the same KE in each trial? Explain.

Investigating How Forces Transfer Energy Part A: Creating a Barrier

Focus Question: What barrier design will stop the car in the shortest distance?

Your task is to create a stopping barrier out of dominoes that will stop the car in the shortest distance possible.

7.5 cm tall

Investigating How Forces Transfer Energy Part B: Creating a Safe Stopping Barrier

Purpose: How does domino density affect the safety of the driver?

Your task is to create a stopping barrier out of dominoes that will stop the car safely (the domino passenger can not fall over or out of the car) in the shortest distance possible. Hypothesis: If I there are fewer dominoes per unit length than I should have a safer shorter stopping distance.

Summary assignment

• • How did the smallest “safe” stopping distance from Part B compare to the stopping distance in Part A?

Can you think of other materials that would make safer barriers than the ones you made out of blocks? Explain why you think these other materials would make safer barriers?

Materials

• • • • • • • 14 dominoes- plus one for “Bob” 120 cm Track 1 pasco Car 2 2”x4” blocks 2 meter sticks Tape clamp

Data for lab report

• • Once you get a safe trial- you need to repeat that trial 3 times You do not need to report unsafe trials, only the trials that gave you at least 2 out of 3 safe runs.

Analysis

• • For your graph – y axis should be stopping distance X axis should be barrier density (# dominoes/cm)

SAFER Crash Barriers

An excellent application of these concepts is the “soft walls” used by major racing facilities across the nation (Dover International Speedway being one of these). The new

SAFER

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eduction) barriers have revolutionized the sport of automobile racing and made it much safer for both the drivers and the fans.

So how do SAFER barriers absorb energy?

The barriers move upon impact so that the KE of the car is transferred to a very large area of the wall (a large portion of the wall flexes upon impact). The key idea is that no one portion of the wall receives a large amount of the car’s KE. The KE of the flexing soft wall is then transferred to the outer permanent wall and support structure. The materials that make up the wall are not elastic. Imagine what the collision would be like if the wall was elastic! Still other portions of the car’s initial KE are transformed into heat energy and sound energy.