Subject Physics for Engineers (Lab 4)

Subject: Physics for Engineers (Lab 4) Rocket Sled Explore Use the Interactive to explore the following questions: 1. With Friction and Air Drag turned off, describe the effect that an applied force has upon the velocity? Also, draw the force diagram at the right. Label the forces using Fapp for Applied force, Fnorm for Normal force from the ground, and Fgrav for the Weight of the sled. Upon observing the interactives, we can conclude that with Friction and Air Drag turned off, the applied force increased the velocity and is continuously increasing. 2. Now turn off the jets so that there are no horizontal forces acting on the rocket sled. Describe how a moving rocket sled moves when there are no horizontal forces. Also draw the force diagram at the right. Use the same labels as before: Fnorm and Fgrav. As shown in the interactives, the rocket sled moves at a constant speed. The rocket’s velocity does not decrease nor increase; it remains constant. There are no frictions or forces applied in the rocket that may cause it to stop. However, the rocket continues to move. 3. Now stop the rocket sled. What do you have to do to stop a rightward moving rocket sled? (Reloading the page doesn't count as a method.) In order to stop the rightward moving rocket sled, you have to turn on the Friction and Air drag or apply a force in the opposite direction of the motion until the velocity reaches zero. In that way, the rocket sled will stop moving. 4. Draw the force diagram for a rightward-moving rocket sled that is slowing down to a stop. Use the labels Ffrict for Friction force and Fair for Air Drag Force. 5. Can an object be moving to the right even though there are no rightward forces acting upon the object? Yes No If you answer Yes, then describe how the object is moving. If you answered No, then write an apology letter to the people of Europe who just suffered a momentary earth tremor as Isaac Newton rolled over in his grave. Yes, an object can be move in any direction whatsoever, without any forces acting on it at all. Furthermore, if an object is travelling to the right but no rightward forces are acting on it but leftward forces are acting on it, the object will not continue to move to the right continuously. When an object moves to the right, it tends to stay that way until a force changes it. Moreover, motion doesn’t need force, acceleration does. 6. Consider the two resistance forces in this diagram: Friction Force (Ffrict) and Air Drag Force (Fair). Do they ever act in the same direction as the object moves? YES. Experiment for a while before you describe your answer below. Yes, as you can see in the interactive, upon turning these two resistance on, if the rocket is moving in the right direction, the Friction and Air force will both facing on the left implying that they act in the same direction as the object moves. 7. Finally, turn Friction and Air Drag off and try the following: Get the rocket sled moving to the right until the speed-o-meter reaches the red zone. Then reverse the direction of the applied force so that it is directed to the left. Does the rocket sled immediately change direction? NO Explain your answer. No, upon reversing the direction, it will slow down first until it reaches to 0 before changing its direction to the other side. Assessment: Consider the force diagrams below for five different situations. Object A F norm Object B F norm F app F grav Object C F grav Object D F norm F frict F app F grav Object E F norm F frict F app F grav 1. Which object (s) could be moving to the right at a constant speed? Both Object A and C 2. Which object (s) could be moving to the right and speeding up? Only Object B 3. Which object (s) could be moving to the right and slowing down? Both D and E 4. Which object (s) could be moving to the left and slowing down? NONE 5. Which object (s) could be moving to the right? Only Object B F norm F frict F grav