2.) In general, what do most simple machines do? Simple machines make work easier by reducing the force needed.

Transcription

1 Name: Simple Machines Study Guide Force and Work- 1.) To be considered work, you have to have a force and a distance through which the force acts. 2.) What is the formula for work? work = force x distance_ What is the unit for work? joules_ 3.) What does something have to do to be considered a machine? A machine is any device that makes doing work easier. 4.) Decide if work is done for each of the following: (Are the requirements for WORK met?) a. Someone is sitting on a cushion on the floor. Work or NO work b. A baseball is hit into the bleachers. Work or NO work c. Ms. Jarrett holds a doorstop in one place to show you an example of a wedge. Work or NO work d. A little girl is pushed on a swing. Work or NO work Simple Machines Basics 1.) What are the 2 basic types of simple of machines, of which all other simple machines are variations of? Also list the other simple machines in the correct category under the heading. inclined planes & levers Wedge pulley Screw wheel and axle 2.) In general, what do most simple machines do? Simple machines make work easier by reducing the force needed. 3.) Do simple machines make less work? Explain. No. Simple machines make work easier, they do not decrease the amount of work. Simple machines can actually make more work due to friction. 4.) What do we mean when we say machines make work easier? (force vs. distance) Simple machines make work easier to do by decreasing the force required by increasing the distance over which the work is done. 5.) A force applied by a machine to an object is the? a.) resistance force b.) effort force c.) force field d.) Jedi force 6.) A force applied to a machine by a person is the? a.) resistance force b.) effort force c.) force field d.) Jedi force 7.) Simple machines make work easier, however there are 2 exceptions to this rule. What are the exceptions, and in each case, what is the advantage each machine gives us? 1. single fixed pulley changes the direction of a force 2. 3 rd class lever gives us increased speed

2 Inclined Plane 1.) An inclined plane decreases the force needed to lift an object by increasing the distance that force is applied. 2.) In general, less force = more distance, and more force = less distance 3.) If the force required to lift a barrel into the back of a truck was 124 Newtons without a simple machine, what would the force required to get the barrel into the back of the truck using a ramp? (Think in general, you don t have enough info to calculate.) a.) less than 124 Newtons b.) more than 124 Newtons c.) 124 Newtons 4.) Inclined planes can increase the amount of work done due to friction. 5.) If it takes joules of work to lift a barrel into the back of a truck without using a simple machine, how much work would be required to get the barrel into the back of the truck using a ramp? (Think in general again, and CONSIDER FRICTION) a.) less than Joules b.) more than Joules c.) Joules If we consider friction, we can conclude that the work would be slightly more due to the friction. Lever 1.) A lever turns on a fixed point, called the fulcrum. 2.) Other than multiplying a force, what else can levers do? Change the direction of a force 3.) Explain how you would determine what class a lever is. (Look where and be what?) Look in the middle and be FRE --- fulcrum in middle = class one, resistance in middle=2, effort in the middle = class 3 4.) What happens to the force needed to move an object as you increase the length of effort arm? force needed would DECREASE as you increase the effort arm 5.) What would happen to the force required if you decreased the length of the effort arm? If you decreased the effort arm, the force needed would increase 6.) True or False and explain- ALL LEVERS make work easier. FALSE. The third class lever does NOT make work easier. They give you increased speed. 7.) Label the effort, resistance and fulcrum in the pictures below an identify what class of lever it is.

3 Pulley 1.) Pulleys can multiply a force or change is direction. 2.) What are the three types of pulleys? Single movable, single fixed, block and tackle 3.) How do you find the mechanical advantage of a block and tackle? Count the sections of rope supporting the weight 4.) True or False and explain-all PULLEYS make work easier. FALSE. Fixed pulleys do not make work easier, they only change the direction of the force. 5.) How does the distance of the string you pull compare to the distance the weight is lifted when using a block and tackle system? The distance of the string you pull is much greater than the distance the object is lifted. (Trading increased distance for decreased force.) 6.) What is the MA of a single fixed pulley? 1 single movable pulley? 2 7.) Find the effort force required to lift the 300 N weight in the diagram N N Simple vs. Compound Machines (mentioned in machines reading) 1.) What makes something a compound machine instead of a simple machine? Composed of 2 or more simple machines 2.) Label each machine with S for simple and C for compound. a. scissors C d. pry bar S b. ramp S e. bicycle C c. single fixed pulley S f. shovel S 3.) List 3 of your own examples of compound machines. (Remember: Machines help make WORK easier. Bull dozer, wheelbarrow, nail clippers, etc Mechanical Advantage Basics 1.) Mechanical advantage is how much the machine multiplies your force. 2.) What does it mean about a machine if it has a mechanical advantage of 1? The machines doesn t increased your effort/ input force. The force the machine applies to an object is the same as the force you put in. It doesn t help you by making you stronger. 3.) Would Machines with higher mechanical advantage would take more or less effort force to make something move? A.) more b.) Less c.) the same

4 4.) Would machines with higher mechanical advantage would take more or less work to make something move? A.) more (with friction) b.) Less c.) the same 5.) If you have a choice between a machine with a MA of 4 and a machine with an MA of 6, which machine would it make more sense to use? MA of 6 you would not have to use as much effort force Wheel and Axle- 1.) Object with larger radius= wheel, object with smaller radius= axle 2.) What would be easier (take less force) to turn and why: An axle with a diameter of 10cm using a 100cm wheel An axle with a diameter of 10cm using a 50cm wheel Why?- It has a larger effort wheel (large wheel). When you increase the effort distance, you decrease the effort force needed. 3.) What would require the least amount of work to turn and why: An axle with a diameter of 10cm using a 100cm wheel An axle with a diameter of 10cm using a 50cm wheel Why?-Both amounts of work are the same due to the axles being the same. The 100cm wheel would just be easier because it travels a greater distance. 4.) Calculate the IMA for the following machines. Show your work. Rw = 11 cm Ra = 0.5 m dw = 2.4 m Ra = 3 cm Rw = 3 m da = 0.8 m IMA=3.7 IMA = 6 IMA = 3 The Screw- 1.) Which of the screws to the right (A or B) would require the greatest amount of force to drive into a piece of wood? Why? A There are less threads so there is less distance. There is more force required for a screw with less distance. 2.) Which of the screws to the right (A or B) would be the easiest to drive into a piece of wood? Why? B There are more threads so there is more distance. Since the rule is the greater the distance, the less the force, there is LESS force required for the screw with more threads. 3.) Which of the above screws (A or B) would have the greatest mechanical advantage? B more threads, more distance, less force 4.) What is a specific advantage we discussed of using a screw instead of an inclined plane? (Think staircases) completing the same goal using a smaller space

5 The Wedge 1.) What does the wedge do as it moves into a material? Separates the material 2.) Of the two wedges to the right, which do you think would require the least amount of force if you wanted to separate those objects 8cm and why? B- it has a greater distance (length) and the rule is when you increase the distance, you decrease the force (make work easier) 4.) What is a major difference between the wedge and an inclined plane? The wedge moves 3.) Measure and calculate the IMA of the wedges. Height = 2.6 cm Slope = 2.4 cm IMA = 2.4cm/2.6 cm =.92 Height = 1.8 cm Slope = 3 cm IMA = 3 cm/1.8 cm = 1.7 Calculations: Show your work! You will be given the following on your test: Work = force x distance Length of slope IMA wedge = FR DE Height or thickness Radius wheel MA x FE IMA x DR IMA wheel and axle = MA = Resistance Force Effort Force I.M.A = Effort Distance Resistance Distance 1.) A clown is trying to lift a refrigerator full of wigs a height of 2M. It would take him a force of 60 Newtons to lift the fridge without a simple machine. a.) Exactly How much work would be required to lift this fridge of wigs without a machine? Radius axle Force= 60 N Distance= 2 M Work = Force x Distance W= 60 Newtons x 2 M Work= 120 Joules b.) Assuming no friction, how much work would be required to lift the fridge of wigs with a lever that has a mechanical advantage of 6? 120 joules the amount of work would not change by using the machine, the work would just be easier c.) Assuming no friction, how much effort force would be required to lift the fridge of wigs with a lever that has a mechanical advantage of 6? 60 N / 6 Force = 10 N

6 2.) What is the force needed to lift a magic school bus if you use a lever with a mechanical advantage 25. The force required to lift the magic school bus without a lever would be 1000 N. Resistance= 1000 N Effort=? M.A = 25 M.A = Resistance effort or effort= resistance M.A 25 = 1000N Effort or Effort=1000N 25 M.A = 40 3.) How much work is being done by a penguin pushing a purple piano with a force of 50 N up a ramp that is 8 meters long? Force= 50 N Distance= 8 M Work = Force x Distance W= 50 Newtons x 8 M Work= 400 Joules 4.) What is the mechanical advantage if a unicorn uses its horn as a lever to open a door 2 feet wide using 300 N of force, which would normally take about 900N to open without a simple machine? Resistance= 900 N Effort= 300 N M.A =? M.A = Resistance effort M.A = 900 N 300 N M.A = 3 5.)How much work is required to lift a bag of cat litter 2 meters, if the bag has a force of 40N? Force= 40 Distance= 2 M Work = Force x Distance W= 40 Newtons x 2 M Work= 80 Joules 6.) Melvin the mighty monkey is trying to get a big bag of bananas into his tree house. It takes 90 Newtons of force to lift into a tree without using a simple machine. He then makes the work easier by putting a ramp that is 10 feet long up to his tree house, which allows him to move the bag of bananas with 10 Newtons of force. What is the Mechanical Advantage of this inclined plane? Resistance= 90 N Effort= 10 N M.A =? M.A = Resistance effort M.A = 90 N 10 N M.A = 9 7.) What is the Ideal Mechanical Advantage of a lever whose effort arm measures 55cm and whose resistance arm measures 5 cm? Resistance= 5 cm Effort= 55 cm I.M.A Lever =? I.M.A= Effort Arm Resistance Arm I.M.A = 55 cm 5 cm I.M.A = 11 8.) What is the Ideal Mechanical Advantage of an inclined plane that has a length of 400cm and a height of 50cm? Resistance= 50 cm Effort= 400c m I.M.A Lever =? I.M.A= Effort dist(length) Resistance dist(height) I.M.A = 400 cm 50 cm I.M.A = 8 9.) What is the ideal mechanical advantage for a lever whose fulcrum is at 20cm? Resistance= 20cm Effort= 80cm I.M.A Lever =? I.M.A= Effort Arm I.M.A = 80cm Resistance Arm 20 cm I.M.A = 4