# Speed/Velocity Measurement

Hi all.
I've been thinking of how one can measure the speed (& indirectly velocity, since we know it's direction of travel) of an object. The object is not necessarily an airplane or an automobile since they've their special devices built for velocity measurement.
I was thinking of measuring my speed while me running a few miles or velocity of a ping-pong ball thrown in a particular direction. Can we build a device for measuring speeds of these objects? Or are there already devices for measuring speeds of arbitrary objects?
Cheers.

Simon Bridge
Homework Helper
Yes there are commercially available devices for measuring speeds of objects - some are quite specific like the speedometer of your car and others are very general like the doppler radar the police use to nab speeding motorists.

You can even get a speedometer app for a smart-phone that uses (I guess) gps or inertial tools.

So I'm puzzled by your question - surely everyone's heard of a speedo?

I was thinking of measuring my speed while me running a few miles
... sure, you time how lino it takes to pass regulary spaced markers like lamp-posts
or velocity of a ping-pong ball thrown in a particular direction.
photography is usual for this, or a photogate. In general you could use sonar or radar.

Hi Simon!!
As I mentioned in the post I know about the speedometer of a car or venturi-meter for measuring the speed of an airplane.
Yes the answer that I was looking for lies in your second quote -

Bobbywhy
Gold Member
Baseball pitchers throw baseballs that are sometimes said to exceed 100mph. How do you imagine that is measured?

Simon Bridge
Homework Helper

By filming them with a high speed camera against a stripy background then comparing the shots frame-by-frame. Knowing the distance the ball travels between shots (because you know the distance between the stripes) and the time between shots tells you the speed. I thought everyone was familiar with this method but it seems another one of my assumptions bites the dust :)

Clearly not everyone has seen Mythusters ...

That would be the photography option - there is always just pointing a radar gun at the pitcher. The pitcher could pitch the ball through a photogate - knowing the time the gate is interrupted and the diameter of the ball tells you the speed.

In general, anything that allows you to divide distance traveled by the travel time will tell you the speed. The idea is to pick one that suits the object in question.

Bobbywhy
Gold Member
Enter into the Google search term box “baseball speed radar” and lo and behold, how many different methods and types of speed measuring equipment are available? To measure baseball speeds, one typically stands behind the catcher with a hand-held doppler radar. Some units can detect and measure ping pong balls, too!

Mount the radar on the glove to measure baseball speed:

Mount the radar on the bat to measure the bat speed:
“The Swing Speed Radar™ from Sport Sensor measures baseball/softball bat speed to help players optimize their swing mechanics. Determine your optimum swing and bat selection for your best distance, quickness and bat control/ball contact.”

Here the sensor is inertial (that is, not radar) and totally contained inside the baseball:
The Laser-Ball Baseball LB-10 can sense if it is being held in your hand and you can hold the ball naturally. Once you pitch the Laser Ball Baseball Radar, it will notice immediately. When the Base Ball Laserball LB 10 is caught, the speed of the Laser Ball is displayed instantly.
http://www.opticsplanet.com/primary-simulation-laser-ball.html

There are laser operated speed measuring equipments as well.

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Hey thanks simon & bobby..

Simon Bridge