Try to define what uniform circular motionuniform circular motionuniform circular motion is? What are its characteristics? Give some examples of uniform circular motion from daily life.
Some possible answers.
The movement of any point on the globe.
A chair of a rotating chain carousel.
The tip of seconds’ hand of a watch.
Uniform circular motion
Definition: Uniform circular motion
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Uniform circular motionuniform circular motionUniform circular motion is a motion along a circular path of a given radiusradiusradius. In uniform circular motion the speed remains constant, but the velocity direction changes. Speed is a magnitude of a velocity vector.
Direction of velocity is always tangent to the circle.
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Period
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Circular motion is periodicperiodicperiodic. It means that the motion occurs at regular time intervaltime intervaltime interval called the period. The symbol for the period is T. The periodperiodperiod is the time for one complete revolution. Period is measured in seconds.
Period
Definition: Period
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PeriodperiodPeriod - time required for one complete circulationcirculationcirculation.
Frequency
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Whereas the period is the time an object takes to make a complete circle, the frequencyfrequencyfrequency is the number of revolutions the object makes per unit of time. The frequency f is the reciprocal of the period:
Frequency is measured in hertz (Hz):
Frequency
Definition: Frequency
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FrequencyfrequencyFrequency - number of revolutions the object makes per unit of time.
Linear velocity
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In uniform circular motionuniform circular motionuniform circular motion, an object covers the same length of the arc segment of a circle in each second of time. The distance covered in one complete revolution around the perimeter of a circle is equal to the circumferencecircumferencecircumference of the circle.
A bicycle wheel shown below is rolling for one complete rotation. The position of a dot on the circumference of the wheel changes continuously and comes back to the same position after one complete revolution.
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The linear velocity in uniform circular motion can be determined as the ratio of the length of the covered arc segment s to the time t in which it was covered:
For one complete revolution:
where r is the radiusradiusradius of a circle, and T is the periodperiodperiod and .
This formula can be rewritten using the frequencyfrequencyfrequency instead of the period:
The linear velocity in uniform circular motionuniform circular motionuniform circular motion is identical to the magnitude of the velocity vector - speed.
Exercise 2
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A small plastic airplane is held on a string and the child spins it over and over again. If the radiusradiusradius of its circle path is 1 m and its periodperiodperiod is 1 s, what is its speed?
6,3
Task 1
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You want to calculate what speed a bicycle wheel can reach. Plan an experiment scenario and explain what should be done to measure all necessary quantities.
Remember
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Uniform circular motionuniform circular motionUniform circular motion is a motion along a circular path of a given radiusradiusradius.
In uniform circular motion the speed remains constant, but the velocity direction changes.