to determine the quantities describing uniformuniformuniform circular motionmotionmotion.
RqNgIbL1dHA3t1
Before you start, answer the question.
What quantities describe uniform circular motion?
REE5uIMTxwi2Y1
Do the following simple experiment.
Simple experiment
Experiment 1
Research problem
What will happen if centripetal forceforceforce stops working.
Hypothesis
If the centripetal forcecentripetal forcecentripetal force does not act anymore, an object will change the path of its motion.
You will need
Glass (transparent mug), small ball.
Instruction
We cover the ball with a glass and move it around the circle. When the ball moves in a uniform motion, we raise the glass up. We observe the movement of the ball.
Summary
For the body to move in a circle, the centripetal force must act. In this case, the centripetal force is exerted on the ball by the glass’s surface. When the glass is raised up, the source of force does not exist anymore and the path of motion changes.
Centripetal force
RtjCWv1qcEZ9C
In the uniform circular motion, the direction of velocity is constantly changing, thus the acceleration vector is non‑zero. According to the first rule of dynamics to change the state of the body movement, in this case the direction of the velocity, a certain force must act on this body.
By Newton’s second law, accelerationaccelerationacceleration is linked to a force by the formula:
In uniform circular motionmotionmotion a force is directed toward the centre of curvature of the path. This force is called the centripetal forcecentripetal forcecentripetal force. “Centripetal” means “centre seeking” force. This force is described by the formula:
where v is the velocity of an object and r the radius of the circle.
R10qTZsmIdqy9
RfMpFdvo7BEjb1
A centripetal forceforceforce acts on a whirling object on a string. If the string breaks, the object will continue its motion along a tangent line.
R1N4rFCL98odl
Exercise 1
RxfTNjvwHrT551
What centripetal force must act on a body moving in a circle with a constant radius if we want to double its speed? Provide some calculations to justify your answer.
The force must be four times greater.
Exercise 2
RdXt6HFppkiRY1
If a 150 g plastic ball is tied with a string of length 1,5 m, and it is spinning with the speed of 30 , what is the centripetal forcecentripetal forcecentripetal force acting on it?
F = 90 N
Centripetal force versus centrifugal force
Centripetal force
Definition: Centripetal force
RzcUzgp9zSk5R1
Centripetal forcecentripetal forceCentripetal force is directed toward the centre of a circle. This force keeps an object moving in a circular path at uniformuniformuniform speed.
Centrifugal force
Definition: Centrifugal force
R15eYMjZSazgP1
Centrifugal forcecentrifugal forceCentrifugal force is an inertial force that occurs only in non‑inertial reference frames, in this case in a frame relative to an object in circular motion.
R1WhKGRawJ9un1
While centripetal force is an actual forceactual forceactual force, centrifugal forcecentrifugal forcecentrifugal force is defined as an apparent force. When an object is spinning on a string, the string exerts an inward centripetal force on the mass, while mass appears to exert an outward force on the string.
Both forces can be determined using the same formula. When an object is rotating uniformly, these two forces will be equal.
Remember
Rk04lKlJMrPK11
In order to keep the body moving in a uniformuniformuniform circular motionmotionmotion, the force directed to the centre of the circle must act on it. This force is called centripetal forcecentripetal forcecentripetal force.
Exercises
R15mJkEF5LKzG
Exercise 3
Exercise 4
Anna is holding on to the outer edge of a carousel with the diameter of 1,8 m. Anna's weight is 40 kg and the velocity of the carousel is 2,5 m/s. What is the centripetal force?
F = 277,8 N
Exercise 5
Explain in English what uniform circular motion causes.