Reading Quiz 6 Key

Did you complete the reading assignment?

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KEY CONCEPTS:

1) The angle of inclination of a plane determines the direction of the normal force acting on objects.

2) Simple machines, like pulleys can be used to decrease the force needed to perform tasks.

Exercise 1

Last reading quiz we looked at forces being applied to frictionless, flat surfaces. When that frictionless surface is inclined, the normal force is now no longer acting straight up against an object. To see how this affects an object, look at the following applet: hhttp://www.walter-fendt.de/ph14e/inclplane.htm

In the applet there are 2 settings to change between; they are spring scale and force vectors. Spring scale gives a qualitative look at how much force it takes to pull the object up the inclined plane. Force vector shows the free body diagram for the object as it is pulled up an inclined plane. You can change the angle of inclination and the weight of the object being pulled up the incline, but keep the coefficient of friction at zero. It also gives the parallel component of force pulling the object up the plane, the normal force acting on the object, and the amount of force it takes to pull the object up the incline. To pull the block up the incline, just press the 'Start' button, to do another run, you will need to press the 'Reset' button before changing values and pulling another object up the incline.

Pull the object up an inclined planes of varying angles of inclination. How does increasing the angle of inclination affect the force needed to pull the object up the plane?

Increases necessary force
Decreases necessary force
Necessary force stays the same

When the plane is inclined to 90 how does the force needed to pull the object up the plane compare to the weight of the object?

Necessary force is greater than the weight
Necessary force is less than the weight
Necessary force and weight are the same

Is it advantageous to push an object up an inclined plane when you need to lift it onto something? If so, how?

Yes, you need to apply less total force to lift it to the new height, although you will need to apply that force for a longer time to get it to the desired height.

Exercise 2

Pulleys can also have an impact on how an applied force can act affect an object. If used correctly, pulleys will give a mechanical advantage, which for now we will use a simplified definition; mechanical advantage means it takes less applied force from a person or machine to perform a task than acting on it directly. To see how this works, go to the following applet: http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=8/a>

This applet is really easy to use. Just double click on a mass attached to a pulley to decrease its mass by one or right click on it twice to increase its mass by one. There are 3 different sets of pulleys. The first uses just one pulley, the second uses two pulleys, and the third set uses the last four pulleys. In each case, consider the mass all the way to the right to be the applied force.

What is the ratio of mass applied to mass the most mass that can be suspended in the one pulley system?

1:1
2:1
3:1
4:1

What is the ratio of mass applied to mass the most mass that can be suspended in the two pulley system?

1:1
2:1
3:1
4:1

What is the ratio of mass applied to mass the most mass that can be suspended in the four pulley system?

1:1
2:1
3:1
4:1

How is it that arranging pulleys in the correct way can produce this kind of mechanical advantage?

Setting up the pulleys in this way increases the number of times the rope/string is pulling up on the masses, so the tension force caused by the last mass acts upward on the other masses as often as the pulley directs the force in an upward direction.