3.5 Relative Velocity in Two Dimensions Relative Motion |
| Instructions: Click on the "Start Simulation" button to start the applet. Make sure that your mouse is not positioned over the applet. In this case, the applet will show motion relative to person standing on the shore. You will see boats (red ovals) and a 'barge' (thick black line) moving in a flowing river (green) and a person (blue figure) running on the shore besides the river. Small full and open circles in either side of the river and on the shore move at the same speed as the river (in the case of the river) or shore (in the case of the shore.) Note the moving bead positioned on top of the barge. Position your mouse cursor over the river to get the view relative to a person moving along the river with the same speed as the river. You can change the frame of reference anytime by placing the mouse cursor either on or off the river. Clicking the right mouse button toggles the animation on and off. You can change the speed of the various elements in the simulation by first clicking the right mouse button, selecting the info checkbox, then dragging the tip of the arrows to the desired values. Note that a text readout of the value of the velocity is available next to the tip. You can change the direction of the velocity by dragging the tip backwards. You cannot change the speed of the barge or the bead on top of the barge. You can make the person move across the river by changing the lateral component of her (his) speed, clicking on the left leg (next to the number 0.0) and dragging the mouse up or down. You can reactivate the applet by clicking the right mouse button. The "info" checkbox allows you also to view all velocity vectors while the simulation is running. Selecting the "2D" checkbox results in a ball thrown vertically upward from the top of the barge. The path of the ball is also drawn. Navigation: You can come back to this window by pressing the "Close Simulation" button on the bottom frame of the utility. |
| Explanation: This applet illustrates the concept of relative velocity as discussed in chapter 3 sections 4 and 5. You can mimic the situations discussed in examples 3.5 and 3.6 when you use only velocities that are parallel the river. Giving the person a lateral speed will enable you to simulate the motion of the boat in example 3.7 or the motion of the dolphin in example 3.9. The 2D mode illustrates the behavior of a projectile (a ball thrown upward) relative to two frames of reference. The ball obviously follows a parabolic path when viewed relative to ground. The horizontal component of its velocity is then equal to the velocity of the barge, its acceleration is g. |
| Source: Fu-Kwun Hwang Go to the web site and link to the Online Library for further information. |