Category: Momentum

Warm up

What two things need to happen to add energy to a system by working?

Answer

Work requires a force and pushing through a distance.

Classwork

Fine tuning your car

• Fine-tuning your car so it will run at least two meters.
• Tips to make your car run better:
  • Students who used fishing wire seemed to get good results. You may want to swap out your string for fishing wire if your car doesn’t run well.
  • Duct tape seems to work best for attaching your string to your axel.

Record the force your mousetrap applies to your wheels.

• Measure the force at three angles: 45°, 90°, and 135°. Record these values in the table in your packet, then calculate the average.
• Measure the length of your lever arm, then calculate the the distance it travels (half the circumference) by multiply by 3.14 ( π )
• Calculate the work done: average force times the distance.
• Measure the mass of your car on the scale.

Turn in your packet today.

Warm up

A 10 kg box is sliding on friction-less ice at 6 m/s. It hits and sticks to a stationary 10 kg box. What is the speed of the two blocks as they move away stuck together?

Answer

Conceptually

Since the combined mass is twice the original mass, the speed must be 1/2 of the original speed, so the two blocks are going 1/2 of 6, or 3 m/s.

Mathematically

• Momentum initial must equal the final momentum
• Initial momentum is 10 kg * 6 m/s = 60 kgm/s
• Final momentum must be 60 kgm/s
• p = m*v so…
  • 60 kgm/s = 20 kg * speed final
  • (60 kgm/s) / (20 kg) = 3 m/s.

Today

• Last in-class build day.
  • If you do not finish today, you must come in at lunch or 7th period to finish your car.
  • Cars are due by Friday, when we will test them out.
• Don’t forget the photo assignment due next Wednesday.

Warm up

If a bug collides with a car, does the car slow down (even a tiny bit)?

Complete the worksheet.

File Name: Momentum-in-collisions.pdf

Download File

Warm up

Momentum: p = m v

Have your Mousetrap car out to Page 4 so I can stamp that you have completed that page.

Calculate the mass of a mousetrap car that has a speed of 2 m/s and a momentum of 1 kg*m/s. Calculate the speed of a ball that has a mass of 0.5 kg and a momentum of 2 kg*m/s. Write out the equations then solve them.

Answers

• Part 1: Mass = 0.5 kg
• Part 2: Speed = 4 m/s.

Classwork

Continue working on your car. You should have it complete by today. Work on Page 5, through Number 14.

Tomorrow I will stamp

Warm up

In your own words, define the word momentum. Next, give an example of two objects where one has more momentum than the other.

Today you will be learning about momentum. Most people have a natural grasp of what momentum means…so remember that as we begin our study. You may have some mistakes in your knowledge, and you may not know the math formula, but I bet you could describe two things that have different momenta (the plural of momentum is momenta).

Class work

1. Complete the warm up.
2. While watching the videos, take notes on the handout. The teacher can pause it if you need it (handout is at the bottom for students who are not in class today).
3. Read pages 374-377 in the textbook. Answer the questions on the handout as you read.
4. Complete the practice problems.

Video 1

Watch the first 3:41 minutes of this video.

Video 2

Play this video all the way through.

Book reading

Read pages 374-377 in the textbook, then answer the rest of the questions and problems on the worksheet.

Video 3

If there is extra time in class, this video introduces momentum in collisions.

Hint: A “vector quantity” just means you have to pay attention to the direction. You’ll spend more time on vectors later in math, but all you need to remember is that you can have positive or negative momentum if they are going in opposite directions.

Elastic collisions are ones where the two objects bounce off each other and don’t stick. Inelastic collisions are where they stick together and move as one object after the collision.

Download File

Warm Up

Which has more momentum? A huge truck stopped in the parking lot or a bee flying towards you? Explain why.

Classwork

Today and tomorrow and tomorrow we will look at earthquakes.

Today’s video: Japan’s Killer Quake, by NOVA

Https://www.pbs.org/wgbh/nova/videos/japans-killer-quake

As you watch this video, please hold in your hearts the 230,000 people who died from the earthquake and tsunami.

Worksheet assignment

Download File

Other notes from today’s video

• Earthquake ‘P’ waves travel about 1-14 km/sec.
  • P stands for primary since they arrive first.
  • These waves are longitudinal/compressional waves.
• ‘S’ waves travel at about 1-8 km/s, and are the more damaging ones.
  • S stands for shear, but also for secondary (since the arrive second)
  • These waves are transverse waves.
• The earthquake struck about 60 miles off the coast.
• Warnings on all cell phones across Japan. The US is developing this warning system for the west coast.
• In the nuclear power plant that was damaged, nuclear energy (stored in uranium) is converted to thermal energy, then to kinetic energy, then to electrical energy.
• Waves reach Tokyo 100 seconds after the Quake, city had one minute warning. Earthquake lasted for five minutes in Tokyo
• Liquefaction is when moisture in earth is compressed and squeezed out–sort of like squeezing a sponge.
• Tsunami was about 3 feet high, 60 miles in length.
• Tsunami can travel over 500 MPH.
• In the ocean, the wave is not ‘cresting.’ Just like normal waves, they usually crest as they reach short.
• Wavelength of the tsunami was long.
• ‘Miyaku’s high walls are useless’ True or not true?
  • Land dropped up to three feet in some places. This made the walls less useful, but it still decreased the damage.
• Tsunami waves retreat, just like regular ocean waves, and when they do the pull people and debris out with it.
• Tsunami reached Hawaii and surged for over an hour. Wave strong enough to cause major damage, but tsunami warning system allowed people to evacuate.
• As tsunami spreads, energy spreads out and so any particular location receives less energy. Circumference of a circle is 2 π r, so if the tsunami travels 2 times as far, it’s twice as powerful at any one given point on that new circle.
• Aftershocks are less than the original earthquake, but some reach 6.2 since the initial Quake was 9.0.
• Japan’s latitude is about equal to Northern California.
• Formation of hydrogen gas (from water, also creates oxygen), lead to explosions that opened the containment buildings.
• ‘Read to go’ in geologic time can be one second or 100 years.
• Along the west coast, from Washington State to Northern California (near Eureka), the Cascadia fault is a ‘subduction fault’ like that in Japan.
• The rest of California has the San Andreas Fault, which is a ‘strike-slip’ or ‘transverse’ fault; the magnitude of earthquakes on these types of faults is about 10 times less than subduction faults.

Videos of the tsunami reaching North America