The velocity is tangential (perpendicular) to the trajectory.
We'll pick a point close to A and label it C then draw an arrow perpendicular to the radius.
The arrow labeled represents the velocity of the bob at point C
A pendulum bob swings back and forth. At the instant shown, the bob is at one of the turnaround points, labeled A. The other turnaround point, labeled B, and the bob’s trajectory (dashed) are shown.
a. Choose a point slightly after point A, and label it point C. Draw a vector to represent the velocity of the bob at point C.
b. Determine the change-in-velocity vector v between points A and C.
c. How would you characterize the direction of v as point C is chosen to lie closer and closer to point A?
d. Each of the following statements is incorrect. Discuss the flaws in the reasoning.
i. “The acceleration at point A is zero. As point C becomes closer and closer to point A, the change-in-velocity vector becomes smaller and smaller. Eventually, it becomes zero.”
ii. “At point A, the acceleration makes an angle with the tangent to the trajectory that is greater than 0° but less than 90° because the trajectory is curved and the object is speeding up.”
e. On the diagram at right, draw arrows at points A and B to indicate the direction of the acceleration at those points. (Hint: Your answer should be consistent with your answer to parts c and d.) Explain.
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the Simple Harmonic Motion of Pendulums concept. You can view video lessons to learn Simple Harmonic Motion of Pendulums. Or if you need more Simple Harmonic Motion of Pendulums practice, you can also practice Simple Harmonic Motion of Pendulums practice problems.
What professor is this problem relevant for?
Based on our data, we think this problem is relevant for Professor Stephanik's class at UW-SEATTLE.