Velocity is the rate of change of an object involving both its speed and direction of motion. You are probably already familiar with speed, which is how fast or slow an object is going. The speedometers in cars tell drivers how many miles or kilometers they would cover in an hour if they drove at the same rate for the entire time. Drivers and objects are constantly changing their speed, however. When the driver presses his foot down on the gas pedal, the car accelerates. Acceleration is when an object changes its velocity. You might feel pushed back into your seat. Any influence that causes an object to undergo a change is called a force. When a driver suddenly hits the brakes, you experience deceleration. When you are being driven along at a constant speed, you don’t feel any kind of acceleration. Your stomach is the best indicator of whether you are experiencing acceleration or not. Too many changes in velocity can make you carsick.
Before you go to an amusement park, you should understand circular motion, especially if you get motion sickness. The velocity you experience during circular motion is calledtangential velocity.Many of the spinning rides involve acceleration and force. The kind of force you’ll often feel at an amusement park is centripetal force, which is the force that makes a body follow a curved path. This experiment will allow you to investigate circular motion at home, without getting into a Tilt-A-Whirl.
How does circular motion affect velocity?
- Smooth floor
- Roll of masking tape
- Clear out a wide patch of floor.
- Place the marble inside the roll of tape.
- Grip the outside edge of the roll of tape with the fingers of one hand. Spin the tape in a circular motion on the floor, not lifting it off the ground. The marble should start going around in a circle. How do you think the marble would move when you take the roll of tape away?
- Now, lift the roll of tape and see how the marble travels.
- Repeat several times.
When you lift the tape up, the marble will travel in a straight line away from the tape. Depending on where you lift the tape roll, the marble will travel in different directions, but it will always be a straight line and it always will be away from where the tape roll was.
Many people would predict that when the tape roll is removed, the marble will continue to travel in the same circular path for a while, until it slows down. When you push a marble in a straight line, it keeps rolling in the same direction when you stop pushing it until friction slows it down. Circular motion is more complicated. The tape roll exerted a constant centripetal force on the marble when it was moving on the table, causing the marble to travel a circular path. When you removed the tape roll, the centripetal force no longer balanced against the momentum of the marble, so off it went.
The velocity of an object in circular motion is constantly changing. Even if the object’s speed is constant, the direction of its motion is always changing, which is the other component of velocity. If you tend to get carsick, be aware that centripetal force can also tug on your tummy, so you might want to stay away from spinning, curving rides.
There is an Olympic event, the hammer throw, in which competitors spin around in a circle to create centripetal force and then release a large, heavy weight. The competitor whose “hammer” flies the farthest wins. The athlete builds his velocity and while he is spinning, must aim for the opening in the fenced area to throw the weight. When he releases it, the velocity carries it into the field. Centripetal force is also the reason you can spin a bucket of water over your head without it spilling. Can you think of any other examples of centripetal force?