MacGyver Season 3 Episode 20 Science Notes: No-Go + High-Voltage + Rescue

There aren’t a bunch of hacks in this episode—so that means I can just write about whatever I want.

Smoke Grenade, Oxygen Mask, Sticky Whips.

This is just classic MacGyver stuff. I really don’t have anything to add.

High Voltage Power Lines

Now we are talking. Why are these power lines high voltage? To answer this question, we need to first think about three things: power, voltage, current.

Let’s start with power. This is the rate of energy change (or in this case, energy loss). For an electrical circuit, the power loss is equal to the product of voltage and current.

P = I\Delta V

But wait! There is also a relationship between voltage and current.

\Delta V = IR

Where R is the resistance (in Ohms) of some element. Substituting this definition into the power definition:

P = I^2R

So, here is your answer. You get more power loss with a greater current. That means the best option is to have low current power lines. But if you want to transmit power—you have to make up for this with high voltage. Boom. There’s your answer. OK, technically these power lines are alternating current and voltage, but the main idea still works.

Next question. What happens if you touch a high voltage line. The answer: not much really.

Yes, if you touch a high voltage line AND something else—like the ground then you will get zapped. The thing that really messes up humans is an electric current running through them. If you just touch one line and nothing else, there is no complete circuit. With no complete circuit, there is no electric current. Oh, this is why those birds can sit on power lines. As long as they only touch that one line, they are fine.

Belay from a lock

The key to a belay is friction. This is actually a pretty cool thing—the more turns a rope has around something (like a post), the greater the friction. You can control the amount of friction between the pole (or padlock in this case) and the rope by slightly varying the amount of rope around the pole.

I think I need to do an experiment to show this—maybe I will do that later. In the meantime, here is a nice tutorial on belays.

Oh, but what if MacGyver wanted to express his anxiety about heights by calculating the impact force if he fell. His calculation might look something like this.

Motorcycle Jump

MacGyver and Desi need to jump a fence with motorcycles. Here’s what he might calculate to find the minimum motorcycle speed to make the jump.

Turn off daytime running lights, or reduce speed? Which saves more?

Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph.

First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com

**Assumptions**

  • The daytime running lights on a car run at about 100 watts (for the pair)
  • The energy density of gasoline is 1.21 x 108 Joules/gallon.
  • A car is 20% efficient at converting this energy to mechanical energy.
  • The alternator is 70% efficient at converting mechanical energy into electrical.
  • At highway speeds, air resistance is the dominating factor in fuel efficiency (this might be wrong)
  • The air resistance can be modeled as Fair = (1/2)?CAv2
  • I will assume an “average” car that has combined CdA of 9 ft2 or 0.84 m2 (where Cd is the coefficient of drag and A is the cross sectional area. Also ? is the density of air, about 1.2 kg/m2)
  • An average trip of 50 miles (I completely made this up).
  • My mythical “average” car gets 25 mpg when going 70 mph

Continue reading “Turn off daytime running lights, or reduce speed? Which saves more?”