Presentation on theme: "Types of Levers First Class: fulcrum located between effort and resistance forces, used to multiply force. If a large force is used on shorter end it can."— Presentation transcript:
1Types of LeversFirst Class: fulcrum located between effort and resistance forces, used to multiply force. If a large force is used on shorter end it can multiply distance.
5Third class leversThe effort force is located between the resistance force and the fulcrum.Effort arm is always shorter that the resistance armCan’t multiply force and it’s MA is always less than one.
7PulleysWorks like a first class lever, uses a rope instead of a bar and the axle acts like the fulcrum. Two sides of pulley are the effort arm and the resistance arm.Fixed: can change the direction of force but doesn’t multiply the effort forceMovable: multiplies the effort force, MA >1 effort distance must be greater to conserve energy.
8Using machinesA combination of two or more simple machines is a compound machine. Ex) axe- wedge & leverBicycle: Overall mechanical advantage is the ratio of the resistance force exerted by the tires on the road to the effort force exerted by the riders feet.
9Now…apply thisUse at least four steps to design a device that performs a simple task. Draw it out. Use simple or compound machines.
10Efficiency Machines can never reach 100% efficiency A measure of how much of the work put into a machine is changed to useful work put out by a machine.Efficiency= Wout X 100% = Fr X drWin Fe FeMachines can never reach 100% efficiency
11Gravitational Potential Energy PE = mghMass, m =Height, h=Free-fall acceleration, g= 9.8m/s2Ex) a 65 kg rock climber ascends a cliff. What is the climber’s gravitational potential energy at a point 35m above the base of the cliff?M=65 kg h= 35 m g= 9.8 m/s2PE= (65 kg)(9.8 m/s2)(35m) = 2.2 x 104 J
12Practice:Calculate the gravitational potential energy in the following systems:A car with a mass of 1200 kg at the top of a 42 m high hillA 65 kg climber on top of Mt. Everest (8800 M high)A 0.52 kg bird flying at an altitude of 550 m
13Practice:Lake Mead, the reservoir above Hoover Dam, has a surface area of approximately 640 km2. the top 1 m of water in the lake weighs about 6.3 X 1012 N. The dam holds that top layer of water 220m above the river below. Calculate the gravitational potential energy of the top 1 m of water in Lake Mead.PE=(6.3 X 1012 N)(220 M)
14PracticeA science student holds a 55 g egg out a window. Just before the student releases the egg, the egg has 8.0J of gravitational potential energy with respect to the ground. How far is the student’s arm from the ground in meters?h = PE/mgPE=8.0 Jm = .055kgg= 9.8 m/s215m
15PracticeA diver has 3400 J of gravitational potential energy after stepping up onto a diving platform that is 6.0 m above the water. What is the diver’s mass in kilograms?M= PE/ ghPE= 3400 Jg = 9.8 m/s2h = 6.0 m3400J/ (9.8 m/s2 )(6.0 m) =m =58 kg
16Bonus:A spider has J of gravitational potential energy as it reaches the halfway point climbing up a 2.8 m wall. What is the potential energy of the spider at the top of the wall?(hint- you don’t need to find the mass!)0.16J
17Bonus:A 0.50 g leaf falls from a branch 4.0 m off the ground to a bird’s nest 2.5 m off the ground. How much gravitational potential energy did the leaf lose?J
18Kinetic EnergyKE = 1/2mv2What is the kinetic energy of a 44 kg cheetah running at 31 m/s?mass, m= 44 kgspeed, v= 31 m/sKE = ?KE = 21000J
19Practice:Calculate the kinetic energy in joules of a 1500 kg car moving at the following speeds:29 m/s18 m/s12 m/s
20PracticeA 35 kg child has 190 J of kinetic energy after sledding down a hill. What is the child’s speed in meters per second at the bottom of the hill?3.3 m/sA bowling ball traveling 2.0 m/s has 16 J of kinetic energy. What is the mass of the bowling ball in kilograms?8 kg3.3m/s8 kg