Peoples Physics Concepts

http://www.ck12.org Chapter 5. Centripetal Forces

5.4 Centripetal Force Problems

• Analyze and solve Centripetal Force type problems.

Students will learn how to analyze and solve Centripetal Force type problems.

Key Equations

Centripetal Force

FC=

mv^2

r







m mass (in kilograms, kg)

v speed (in meters per second, m/s)

r radius of circle

Guidance

Any force can be a centripetal force. Centripetal force is the umbrella term given to any force that is acting

perpendicular to the motion of an object and thus causing it to go in a circle. Keep the following in mind when

solving centripetal force type problems:

• The speed of the object remains constant. The centripetal force is changing the direction but not the speed of
  the object.


• Although the object ’feels’ an outward pull, this is not a true force, but merely the objects inertia. Remember,
  Newton’s first law maintains that the natural state of an object is to go in a straight line at constant speed.
  Thus, when you make a right turn in your car and the basketball in the back seat flies to the left, that is because
  the car is moving right and the basketball is maintaining it’s position and thus from your point of view moves
  to the left. Your point of view in this case is different from reality because you are in a rotating reference
  frame.

Applications

• To find the maximum speed that a car can take a corner on a flat road without skidding out, set the force of
  friction equal to the centripetal force.


• To find the tension in the rope of a swinging pendulum, remember that it is thesumof the tension and gravity
  that produces a net upward centripetal force. A common mistake is just setting the centripetal force equal to
  the tension.


• To find the speed of a planet or satellite in an orbit, set the force of gravity equal to the centripetal force.