The TV show MythBusters entered its final season a couple of weeks back (this being mid july 2016 for future referrence) . The greatest part of the show is the fact Adam Savage and Jamie Hyneman aren’t scientists but they still do some awesome science. They show us that everyone can do science—the MythBusters simply have better building skills than most.
As an engineer, I’ve been impressed by the excellent physics demos the MythBusters make. Some of these are classic examples straight from your physics textbook and some are surprising results that no one really saw coming.
Let’s take a look at a few these examples from previous seasons.
1. To Shoot a bullet or to drop a bullet
When you take a look at just about every introductory physics book you will find something like this:
When we are looking at projectile motion, the vertical and horizontal motions are independent. In fact, if you shot a bullet horizontally and dropped a bullet from the same height, the two bullets would hit the ground at exactly the same time.
If your instructor ever chose to do a demo, he/she would have used a couple of small balls at low speed instead of real bullets. But would it work with an actual gun? The myth buster proved this, the answer is “mostly yes”. In a high speed video of this demo, the dropped bullet hits just slightly ahead of the fired bullet—a time difference of just 39.6 milliseconds. Honestly, this is close enough for most, myself included.
But what if you include air resistance on both bullets? Do they still hit the ground at the same time? The answer is no. The dropped bullet will hit the ground first. There is a detailed explanation for this occurrence but that make take a whole article. The short version is that the fired bullet has much more air resistance and this produces more vertical air drag than the dropped bullet.
2. Car Crash; wall crash vs head-on collision
Another classic physics textbook examole or exercise question goes something like this:
A car is traveling at 50 kph. Would it do more damage to crash into a brick (and unmoving) wall or a head on collision with a similar car also traveling at 50 kph?
Most students (I probably would have too) would say that a head-on collision is worse than crashing into a wall. The thinking is that there are two cars in the head-on collision so it should be twice as bad. If it is indeed twice as bad then it should be the same as one car traveling at 100 kph crashing into a wall, a result of our active imaginations. But the maths and real life say otherwise. Consider one car traveling at 50 kph crashing into a wall. The car goes from 50 kph to 0 kph over some time interval. This means the car has a change in momentum due to some external force (from the wall). Now switch to two cars crashing head on at 50 kph. Both cars still go from 50 kph to 0 kph so they each have the same change in momentum (but in opposite directions) requiring the same stopping force. What about a car at 100 kph? Yes, this car would have double the momentum of a single 50 kph car. However, it would have kinetic energy 4 times that of a car at half the speed. One MythBusters episode showed crashing one car at 100 mph is way worse than a head-on collision between two 50 mph cars.
3. Relative velocity.
What would happen if you shot a ball with a speed of 60 mph from the back a car traveling at 60 mph? Would the ball remain stationary? Yup—that’s exactly what the MythBusters did.
This is all about relative velocity. The speed of the ball with respect to the car is 60 mph to the right (negative) and the speed of the car with respect to the ground is 60 mph to the left (positive). This means that the speed of the ball with respect to the ground is 60 mph + (-60 mph) = 0 mph. The math doesn’t seem so complicated, but getting the relative speeds just right isn’t so simple.
There are many more experiments the Mythbusters have demonstrated over the years and many theories have been debunked. If you are intothe physics just for the fun of, its worth a watch. You won't be disappointed!
