I can make value judgements using the concept of momentum

Should Trucks Have Different Speed Limits Than Cars? 👁 

Based on what you know about motion and forces so far, should trucks have different speed limits than cars?

The goal of speed limits is to save lives and lower the deaths from road accidents.

Why do we have differential speed limits?

Why Lower Speed Limits and Truck Speed Limiters Will Save Lives

One big takeaway here is that trucks have a larger mass. Therefore even though the same force is applied to the truck in a collision as to the other vehicle, the felt acceleration is much smaller for the truck. Another way to think about this is momentum. More momentum generally means more inertia (harder to stop this thing once it gets going) and more damage caused in a crash.

The formula for momentum is: p = mv (p - momentum, m - mass, v - velocity)

Trucks have a larger momentum. That means more stopping distance when they slam on the breaks and more damage caused going at the same speed as a smaller vehicle (that has less mass).

 be on an elephant with a mass of 1000 kg traveling at 5 m/s OR would you rather be on a horse with a mass of 500 kg traveling at 25 m/s?

p=mv -> calculate the momentum of each to compare.

I would rather take on the army on a fast moving horse because I’d have more momentum and be able to do more damage.

In the style of the example above, come up with 3 WYR (would you rather) questions and answers based on what you know about momentum so far.

They should be creative and require using p=mv to find the answer.

Skates & Tunnels: A Momentum Problem 🧭 

Elon Musk started the Boring Company in 2016 to build a network of underground tunnels that he hoped would help to fight traffic on city streets. In 2018 the company is working on 4 separate tunnel systems across the US. In early models, skates modeled after the Tesla Model X (see image above) were proposed to move through the tunnel at high speeds on rails to transport everything from pedestrians to cars.

In this project you will act as a member of an engineering team proposing a plan for a tunnel from Outer Mission to SFO airport to San Francisco city officials. First you will ask some questions and analyze data from past experiments to better understand the constraints of the project. Given the constraints, your team will propose a plan by answering two guiding questions:

Of course, there must be clear reasoning for city officials to understand that your team has carefully thought through your proposal. Take care to use physics calculations to weigh options but remember that there are many other considerations as well.

The image above shows some testing done at the MIT Loop Lab. The table below shows data from these experiments. Specifically, the table shows different loads added to the skates, measured in kilograms (kg), for the proposed velocity of 

 (about 124 mph). Crash dummies were used for tests. Wear to the rail system is described indicating physical stress put on the rail line. More stress is unsafe and costly.

Read the setup and data above carefully and write a proposal.

To make your decisions, start by choosing a physical stress on rail that you think would be the most reasonable and calculate the momentum that caused this level of stress on the rail. (From there you can increase mass as long as you decrease velocity proportionally and vice versa) 

What other considerations do you have? (ex. traffic concerns, costs, who would benefit)

Based on your understanding of momentum, the data from the MIT Loop Lab, and any other concerns, propose a skate system that answers the original 2 guiding questions: What load do you plan to carry and at what speed? Explain using specific evidence.

How important would you say helmets are for electric scooter riders? Write an explanation that includes evidence from what you know about momentum. Address the relative mass of an electric scooter vs cars on the road and the relative velocity of an electric scooter vs. other non-powered modes of transportation like bikes. 

Physics · 1 Forces & Motion · 5 Momentum

Why Do Trucks & Cars Have Different Speed Limits?