UniformCircularMotionSE

Name: ______________________________________ Date: ________________________ 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? Draw an arrow on the image to show the yo-yo’s direction. 2. Do you think the released yo-yo’s path will be straight or curved? Explain. _________________________________ _______________________________________________ Gizmo Warm-up 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? __________________ Straight because there is no longer a force acting on the yo-yo (8.00, 0.00) (1.31, 7.89) A

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? _______________ ° Activity A: Velocity, acceleration, and force Get the Gizmo ready: • Click Reset . • Select the DESCRIPTION tab. • Turn on Show velocity and acceleration vectors . 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? 1. 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. A. Given the fact that the puck is accelerating, what can you conclude? ____________ ___________________________________________________________________ B. What is the direction of the force on the puck as it travels in a circle? ____________ No Yes Velocity and acceleration vectors are constantly moving as it rotates around the circle (centripetal force) That’ there is force acting on the puck. F= ma Inwards towards the center of the circle Acceleration vector is pointing to the center of the circle. Velocity vector is pointing away from the circle, making a 90 degree angle

6. Think and discuss: If you are sitting in the back seat of a car that makes a hard left turn, you will feel pushed toward the right side of the car. Why does your body move to the right? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ° Activity B: Centripetal acceleration Get the Gizmo ready: • Click Reset . • Set the radius to 2.0 m, the mass to 1.0 kg, and the velocity to 10.0 m/s. Introduction: The acceleration toward the center that keeps objects in uniform circular motion (circular motion at a constant speed) is called centripetal acceleration . An understanding of centripetal acceleration was one of the key elements that led to Newton’s formulation of the law of universal gravitation. Question: How is centripetal acceleration related to radius, mass, and velocity? 1. Record: Select the BAR CHART tab, select Acceleration from the dropdown menu, and turn on Show numerical values . The bar on the left shows the magnitude of the acceleration, or | a |. The units of acceleration are meters per second per second, or m/s 2 . What is the current magnitude of the acceleration? ________________________________ 2. Predict: How do you think the magnitude of the acceleration will depend on radius, mass, and velocity? Record your predictions by completing each sentence. When the radius increases, the centripetal acceleration will _________________________. When the mass increases, the centripetal acceleration will _________________________. When the velocity increases, the centripetal acceleration will ________________________. 3. Gather data: Keeping the mass at 1.0 kg and the velocity at 10.0 m/s, record the magnitude of centripetal acceleration for each given radius value. Include units. You feel your body move to the right due to Centrifugal Force (being pulled outward) 50 m/s Decrease Stay the same Increase 2

2019 Radius: 2.0 m 4.0 m 6.0 m 8.0 m 10.0 m Acceleration: Radius factor: Acceleration factor: 4. Calculate: To calculate the radius factor, divide each radius by the original radius (2.0 m). To calculate the acceleration factor, divide each acceleration value by the original acceleration (50.00 m/s 2 ). 5. Analyze: How does the acceleration change when the radius is multiplied by x ? __________ _________________________________________________________________________ (Activity B continued on next page)°Activity B (continued from previous page) 6. Explore: Move the mass slider back and forth. Does the puck’s mass have any effect on its acceleration? Explain. _______________________________________________________ _________________________________________________________________________ 7. Gather data: Set the radius to 2.0 m and the velocity to 1.0 m/s. Keeping the radius the same, record the magnitude of centripetal acceleration for each given velocity. Include units. Velocity: 1.0 m/s 2.0 m/s 3.0 m/s 4.0 m/s 5.0 m/s Acceleration: Velocity factor: Acceleration factor: 8. Calculate: To calculate the velocity factor, divide each velocity by the original velocity (1.0 m/s). To calculate the acceleration factor, divide each acceleration value by the original acceleration (0.50 m/s 2 ). 9. Analyze: How does the acceleration change when the velocity is multiplied by x ? _________ _________________________________________________________________________ Acceleration decreases as the radius gets bigger (radius x2, acceleration 1/x) The puck’s mass has no effect on the acceleration. Mass affects velocity and distance When velocity is multiplied by x, then acceleration will be multiplied by x^2 50/ 25m/ 16 67 me 10MIs2 N 234 5 N 7273Y4Y5 - 0 5MK Imis 4 5 M1S"8 rls 12 5 m/s D 2 3 4 5 N H q IP 25