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•IV. Force, Motion and Mechanical Energy •C. Interactions of force and motion •State Standards 1.1; 1.6; 1.10; 3.1; 3.6; 4.1
•7th grade assessment •Students should be able to explain and demonstrate how common tools are simple machines and discuss the forces and motions involved. •View lesson before using with students. Sample questions and answers appear with mouse click or automatically.
What are the six basic kinds of simple machines?
• Inclined plane • wedge • screw • Lever • Wheel and axle • pulley
What are some examples of simple machines?
• Do you know what • Do you use your a seesaw is? bare hands for cracking nuts? • Have you ever used a crowbar? • Why do scissors cut paper? • Have you ever seen a car with a • How does a bat hit flat tire jacked up? a home run?
• Most of the machines in your body are levers that consist of bones and muscles. • How can you bend your arm? • Your biceps muscle provides the input force. The output force lifts your arm. • How can you tilt your head back? • The joint at the top of your neck is the fulcrum of a first class lever. The muscles in the back of your neck provide the input force.
Levers in the body
Point your left index finger (your pointing finger) in front of you. Then move it to the right.
• Where is the fulcrum? • Where is the input force? • What kind of lever is your finger?
How do you find mechanical advantage?
• The diagram of the simple pulley shows how the effort rope and object move. • The distance moved by the effort rope divided by the distance moved by the object. • 60 cm 20 cm = 3
Effort force
60 cm
Output force
Load 20 cm
• Pulley systems can be very helpful in lifting heavy loads with a small effort force. • As the mechanical Output advantage increases, the force effort force required to 300 N lift a load decreases. Load • 300 N 100 N = 3
How do you determine the amount of force necessary to lift objects with a pulley? Effort
force
100 N