Go to http://phet.colorado.edu/simulations/sims.php?sim=Motion_in_2D and click on Run Now.
1) Once the simulation opens, click on ‘Show Both’ for Velocity and Acceleration at the top of the page. Now click and drag the red ball around the screen. Make 3 observations about the blue and green arrows (also called vectors) as you drag the ball around.
1. The green line points in the direction that the ball is going to go
2. The blue line changes the direction it points.
3. The blue line also changes size depending on the speed
2) Which color vector (arrow) represents velocity and which one represents acceleration? How can you tell?
The green line represents velocity because it points in the direction. The blue line is acceleration because as the ball is no longer accelerating it points in the opposite direction.
3) Try dragging the ball around and around in a circular path. What do you notice about the lengths and directions of the blue and green vectors? Describe their behavior in detail below.
When the ball is in a circular path the blue line points towards the middle of the circle, while the green follows the circumference.
4) Now move the ball at a slow constant speed across the screen. What do you notice now about the vectors? Explain why this happens.
The blue line does not appear because when there is a constant speed there is no longer acceleration.
5) What happens to the vectors when you jerk the ball rapidly back and forth across the screen? Explain why this happens.
The green line gets larger and the closer it is to the desired point it gets smaller. The blue line point in the direction that is desired until the ball slows down then it is a positive acceleration in the opposite direction.
6) Now click on ‘Circular’ on the bottom. Describe the motion of the ball and the behavior of the two vectors. Is there a force on the ball? How can you tell? Be detailed in your explanations.
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