A Moment of Science

Don’t Try This at Home!

You're cruising along a desert highway in your souped-up roadster. Unfortunately, you are not paying attention to the signs and zoom off the edge of an mesa.

Here’s a hypothetical scenario that is to remain hypothetical. In other words, don’t do this.

Okay. You’re cruising along a desert highway in your souped-up roadster, leaving the roadrunners in the dust. Unfortunately, you are not paying attention to the signs and zoom off the edge of an enormous mesa. Now here comes the physics.

When you left the edge of the mesa you were moving forward at sixty miles an hour. It seems pretty clear your car will continue moving out for a considerable distance before falling.

But wait a minute, is that right?

The answer is NO. You begin falling the instant your car leaves the mesa, no matter how fast it’s traveling. If you got this one wrong, don’t worry: almost everybody does. For some reason the out-and-then-down scenario seems more sensible to us. But let’s look at it again.

Gravity is always pulling your car downward, even when it’s sitting still on the road. Send the car over a cliff and gravity doesn’t need any time to start acting. It’s already pulling, just as it was before you left the road. But in this case, the car also has a forward velocity.

That velocity will indeed send it flying outward — but not at the expense of falling downward. The result is that your free-falling car will make a graceful arc in the air, moving both downward and outward at the same time.

By the way, you had a parachute and dove out just in time. Close one.

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