Unit 8A: Systems in Action (Pg. 2 85) Chapter 2: Getting to Work (pg. 28 55) Name: Date: 2.1: Physical Systems: Simple Machines (Pg. 30 35): Read Pages 30-35. Answer the following questions on pg. 35: 1. Define the followings: Simple Machine Lever Fulcrum Load Arm Effort Arm A device that requires a single force to work; made of only one or two parts. A rigid bar that pivots at a point called the fulcrum. The pivot point of a lever. The part of a lever that extends from the fulcrum to the mass being moved. The part of a lever that extends from the fulcrum to where the force is applied. 2. Which of the six simple machines relates the most to your everyday life? Explain. The wheel and axle; because it allows me to get around in a car or on my bicycle. 3. Describe the relationship between input force, output force, and load force. The input force is the force applied by the user. The load force is the force that the input force must overcome. The output force is the push that a lever applies to the load. 4. Draw the following classes of levers. Label using the words: Fulcrum (F), load (L), input force, load arm, and effort arm. (See page 32 for help) Input Force Class 1 Lever effort arm load arm L F Class 2 Lever Input Force L effort arm load arm F Class 3 Lever L Input Force effort arm load arm F
2.2: A closer Look at Forces (Pg. 36-39): Read Pages 36 39. Answer the following questions: 1. Define the followings: Please see the TB or PB for the definitions. Force, Magnitude, Newton, Gravitational Force, Mass, Weight, Friction 2. What are the four fundamental forces in nature, according to modern science? a) gravitational force b) electromagnetic force c) strong nuclear force d) weak nuclear force. 3. What changes when you go to the moon: your mass or your weight? Explain. My mass stays the same; my weight changes because the moon has much less gravitational pull or less gravity (W M = 1/6 W E ) 4. A rock has a mass of 8 kg. What is the weight of the rock on Earth? Show your work. (Use g = 10 m/s 2 ) W = m x g = 8 kg x 10 m/s 2 = 80 kg.m/s 2 = 80 N 2.5: The Scientific Meaning of Work (Pg. 46 48): Read Pages 46 48. Answer the following questions: 1. a) What is the formula for calculation work? W = F x d Work (joule) = Force (N) x Distance (m) b) What are the units used in the formula? J = N. m Note that kj = 1000 J 2. How does the Newton-metre compare with the joule? A Newton-meter and a joule are equivalent. Joule is the name of the unit given to the amount of work done when a force of one Newton moves through a distance of one metre. I J = I N x I m 3. Calculate the work done in the following instances: a) pushing a car 15 m using a force of 600 N. W = F x d = 600 N x 15 m = 9 000 J = 9 kj b) lifting a 100 N sewing machine from the floor to a tabletop 75 cm high. Convert: 75 cm = 0.75 m W = F x d = 100 N x 0.75 m = 75 J 4. If you pushed a car 25 m and did 60 kj of work, how much force did you use? Convert: 60 kj = 60 000 J W = F x d F = W = 60 000 J = 2400 N d 25 m 5. Imagine putting yourself in a push-up position and staying there. Assume that neither the floor nor your body moves. You will use a lot of energy but do no work. How can energy be consumed when no work is done? To hold yourself up requires your muscles to use energy. However, the scientific definition of work states that work is equal to a force times the distance that something is moved. Since you are not moving, scientifically, there is no work being done.
2.3: Mechanical Advantage (Pg. 40 43): Read Pages 40 43. Answer the following questions: Important Notes: 1. To find the MA of a machine, use the one of the following formulas: MA = Output force Input force MA Lever = effort arm length load arm length MA pulley = input distance output distance Actual MA = Measured output force Measured input force 2. MA has no units ( a ratio) 3. When the input and the output forces are the same, MA = 1 4. When input force > output force; MA < 1 1. Define the followings: Mechanical Advantage Ideal Mechanical Advantage Actual Mechanical Advantage The ratio of output force to input force for a given machine. The MA of a machine if all of the input force in converted into output force; never possible in real-world application. The MA of a machine in real-world applications; equal to ideal MA minus force lost to friction, slippage, and distortion. 2. Show your work and calculations including the units: a) If an output force is 8 times larger than an input force, what is the mechanical advantage? MA = Output force = 8N = 8 Therefore, the MA is 8. Input force 1N b) In an input of 0.5 N is required to lift a rock of 35 N, what is the actual MA? Actual MA = Measured output force = 35 N = 60 Actual MA = 70 Measured input force 0.5 N
3. a) The MA of a class 3 lever will always be less than 1. Explain why. In a class 3 lever, the input force is located between the fulcrum and the load. Therefore, the effort arm length will always be less than the load arm length and the ration of the effort arm length to the load arm length will be less than 1. Class 3 lever Input Force effort arm MA Lever = effort arm length load arm length L load arm F b) If there is no MA to class 3 lever, why are they considered useful? Class 3 levers have a MA < 1. However, they are still considered useful because the output distance and the speed are increased. 4. What parts of a pulley system will cause the actual mechanical advantage to be less than the ideal mechanical advantage? The parts of a pulley system that might involve friction will cause the actual MA to be less than the ideal MA. This would be where the wheel turns on the axle or where the axle is turning in the frame of the pulley. 5. Use the formulas above to solve the following problems: a) The wheelbarrow has an effort arm 140 cm and a load arm 70 cm long. What is the MA? MA Lever = effort arm length = 140 cm = 2 The MA of the wheelbarrow is 2 load arm length 70 cm b) To lift a load 8 cm with a pulley system, 24 cm of string had to be pulled. What is the MA? MA pulley = input distance = 24 cm = 3 The MA of the pulley system is 3 output distance 8 cm c) Imagine that you are lifting a patio stone using a pry bar as a lever. If the input force applied is measured as 50 N and the output force is measured as 450 N, then what is the actual MA? Actual MA = Measured output force = 450 N = 9 The Actual MA of the pry bar is 9 Measured input force 50 N d) The pulley system is being used to raise a load. The input force on the pulley system is 3 N, and the output force is equal to 18 N. What is the actual MA of the pulley system? Actual MA = Measured output force = 18 N = 6 The Actual MA of the pulley system is 6 Measured input force 3 N
Chapter 2 - Review (pages 54-55) Name: Date: What Do You Remember? 3. Force 1 Force 2 a) Give two forces that require direct contact to have an effect. Friction Mechanical b) Give two forces that do not require direct contact to have an effect. Gravity Magnetic, electrical 4. Draw diagrams of the three different classes of levers, showing the fulcrum, the input force, and the output force for each. 5. a) Name the two components that all forces share. All forces have magnitude and direction. b) How are these components shown on force diagrams? In a diagram, direction is shown by the direction the arrow representing the force is pointing. Magnitude is shown by the length or width of the arrow. 7. a) Define Mechanical Advantage. MA is the ratio of the amount of force that is needed to perform a task without a machine to the amount of force that is required to perform the same task using the machine. b) Explain why there is a difference between actual mechanical advantage and ideal mechanical advantage. Ideal MA is what the MA would be if no input force were lost to friction, slippage, or distortion. Actual MA accounts for this loss of input force. 8. What is the mathematical formula used to calculate work? W = F x d Do You Understand? 10. With a class 1 lever, does MA increase or decrease as the fulcrum is moved closer to the load? Explain why. For a class 1 lever, the fulcrum is between the input force and the load. Moving the fulcrum closer to the load increases the length of the effort arm and decreases the length of the load arm. This increases the MA, which can be found by dividing the effort arm length by the load arm length.
11. What is the approximate weight of a 2L bottle of pop on Earth? Explain. First convert the 2 L (capacity) into Kg (mass). Use g = 9.8 m/s 2 Since 1 cm 3 = 1 ml = 1 g ; and 1 dm 3 = 1 L = 1 Kg; therefore, 2 L = 2 Kg W = m x g = 2 kg x 9.8 m/s 2 = 19.6 N The pop would weigh 19.6 N Solve a Problem: 13. What is the MA of a lever that can lift a 100 N load with an input force of 20 N? MA = Output force = 100N = 5 Therefore, the MA is 5. Input force 20N 14. a) Figure 2 shows a class 1 lever. Calculate the work done to move the load 25 cm. 25 cm = 0.25 m W = F x d = 50 N x 0.25 m = 12.5 N.m = 12.5 J b) Estimate the amount of work done if the fulcrum were moved so that the input force was twice as far from the fulcrum as the load. Explain your answer. The amount of work done would be the same as the amount of work needed to move the lever with the fulcrum in the middle. The lever does not change the amount of work that needs to be done, only the input force needed and distance over which the force is applied. 15. a) Calculate the work done in Figure 3. W = F x d = 4500 N x 1.5 m = 6750 N.m = 6750 J b) Approximately how far will the people have to travel to move the truck 1.5 m? Justify your answer. The output force of 4500 N is about 4 times larger than the input force of 1200 N. To move the truck a distance of 1.5 m, then, the people must move approx. 4 times that distance, or 6 m. 16. A single moveable pulley is being used to move a 140 N load. The pulley is a little dirty, so it adds another 5 N of frictional force. a) Can this load be moved with a 75 N input force? Explain your answer. MA = Output force = 140 N + 5 N = 145 N = 1.93 = 2 Therefore, the MA of the single moveable pulley is 2. Input force 75 N 75 N Yes, a single moveable pulley has a MA of 2, so a 75 N force would be able to move a load that is up to 150 N. The load plus the frictional force totals only 145 N. b) Would a single fixed pulley work? Explain your answer. A single fixed pulley would not work. A single pulley has a MA of 1, so using that pulley with a 75 N input force would only allow movement of an object with a weight of 75 N or less.