Student Exploration: Uniform Circular Motion
Vocabulary: acceleration, centripetal acceleration, centripetal force, Newton’s first law, Newton’s second law, uniform circular motion, vector, velocity
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. A boy is whirling a yo-yo above his head in a counter-clockwise direction. At the exact moment shown at left, he lets go of the string. In which direction will the yo-yo travel?
2.Do you think the released yo-yo’s path will be straight or curved? Explain
The Uniform Circular Motion Gizmo™ shows a pink puck that is floating above a circular air table. The puck is held to the center of the table by a string so that it travels in a circle at a constant speed.
Check that the radius is 8.0 m and the mass is 5.0 kg. Set the velocity to 5.0 m/s.
1. Turn on Show puck position (m). What are the coordinates of the puck’s position?
2. Click Play ( ), and then click Pause ( ) when the puck is close to the y-axis. What is the puck’s position now?
3.Click Reset ( ). Select the BAR CHART tab and select Velocity from the dropdown menu. The three bars represent the magnitude, the x component, and the y component of the puck’s velocity.
A.Click Play. Does the magnitude of the velocity change over time?
B.Do the x and y components of the velocity change over time?
Introduction: Velocity is a vector quantity that describes both the speed and direction of an object’s motion. Vectors are represented by arrows. While the speed of the puck is constant, its direction changes continually as it travels in a circle. Because its direction is changing, the puck undergoes acceleration even though its speed is constant.
Question: How is the velocity of a revolving body related to its acceleration?
Observe: On the SIMULATION pane, observe the directions of the velocity (green) and acceleration (purple) vectors.
A. What do you notice?
B. Click Play. What do you notice about the vectors as the puck moves in a circle?
2.Infer: Newton’s second law states that a force will cause objects to accelerate in the direction of the force.