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We just finished a section on friction

We just finished a section on friction. Now we’re studying circular motion. In studying circular motion:. students often don’t understand what actual forces can fill the role of centripetal force.

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We just finished a section on friction

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  1. We just finished a section on friction

  2. Now we’re studying circular motion

  3. In studying circular motion: • students often don’t understand what actual forces can fill the role of centripetal force. • this activity shows that friction can be the cause of centripetal acceleration (as can gravity, normal force, string tension, etc). • We play some Pink Floyd first. Gets kids thinking that record players may be useful for something.

  4. Using our classroom record player:

  5. we show that friction force can be the centripetal force. • Take measurements and calculate centripetal force and friction force • Convert rotational to linear velocity ( v =𝛱 r² / t • Determine the coefficient of friction (𝜇)

  6. What you need • Turntable, an LP record • Construction paper, compass meter stick, button • Mark paper with concentric circles ( I space circles every 2 centimeters) • Place paper over record on turntable • Set turntable speed to 45 RPM

  7. Find the distance from center at which button starts to slide off. • Place button a small distance from center of record. • Turn player on. • If button doesn’t slide of, repeat, moving button further outward until it DOES slide off. • Record this distance from center .

  8. At this distance,fsmax = Fc • Therefore

  9. To calculate linear velocity of button: • Measure distance (r) of button from center • Determine RPM of player

  10. To calculate coefficient of static friction: • Since static friction force equals centripetal force at this point, • And then,

  11. Skills developed: • Understand that different forces can cause centripetal acceleration • Convert rotational velocity to linear velocity • Find coefficient of static friction

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