Question

In circular motion the body has constant speed but not constant velocity? Why?

Asked by: Heidi

Answer

The physics definition of speed is just distance covered per unit time. The physics definition of velocity, however, is a combination of speed AND DIRECTION. In other words, physics treats speed and velocity as two similar, but distinctly different, concepts. A wind speed, for example, can be given as 10 miles per hour. Its velocity, however, would have to specify that it is 10 miles per hour from the North.

An object following a circular path can be covering the same distance along the circle's circumference with every passing minute, giving it a constant speed. To maintain a circular path, though, its direction must be constantly changing. Since a change in either speed OR direction means a change in velocity, the object's velocity is not constant.

Why is it useful to define velocity that way? Because Newton's laws of motion relate any change in VELOCITY (not just speed) to the application of a net force. Even though circular motion can be at a constant speed, its changing velocity requires that a (centripetal) force be present to deviate from a straight line and maintain its circular path.

Answered by: Paul Walorski, B.A., Part-time Physics Instructor

Search

Loading



Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department

Science Quote

'A theory with mathematical beauty is more likely to be correct than an ugly one that fits some experimental data. God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.'

Paul Dirac
(1902-1984)

Deal of the Day

Image of Hover Craft Kit. Click on this image for more info. Hover Craft Kit
Regular Price: $29.99
Today's Price: $12.00
Learn the science behind hover craft technology with this cool kit! Buy it now! Deal ends at midnight!

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
Slide Making Kit
Top Secret - Spinning Top
Wood Grain Newtons Cradle
Deluxe 3D Mirascope
Solar Radiometer
Periscope
Ultimate Chemistry Set CHEM C3000
Solar Science 4M Kit
3D Magnetic Field Tube