Chapter 10: Movement and Forces 10.1 The skeletal system provides movement and protection 10.2 The muscular system makes movement possible 10.3 Muscles exert forces 10.4 Bones and joints at as levers

Warm-up True or False The biceps exercise a pulling force on your arm. True More force is required to push objects up ramps. Ramps reduce the amount of force needed to move objects. A lever is made up of a rod and an inclined plane. A lever is made up of a rod and a pivot point.

The body uses levers Examples: Lift something close to your body: shoulder muscles apply less force than when you lift something with your arm stretched out A small movement from your muscles moves the end of your arm a large distance What does your arm act like when you lift something with it? A lever!

Levers can change the effects of a force Recall: A lever is a solid bar, or rod, that moves around a fixed point, a fulcrum a bone as a rod a joint as the pivot point bend your arm at the elbow - you are pivoting your forearm around the joint in your elbow

Levers - fulcrum Fulcrum – a fixed point around which the rod of a lever turns The lever’s “pivot point” Can be located anywhere along the rod If in middle – both ends of rod may move If at end – just one end may move Ex: stapler Use less force when pressing… When a force is farther from the fulcrum, it can turn the lever more effectively

Levers - fulcrum Elbow Weight location relative to fulcrum: When a weight is at your wrist–– farther from the fulcrum––it is harder to lift Stapler and hand weight: the force is more effective when it is farther from the fulcrum

Input Force and Output Force Input force: the force exerted on a machine Often called the “effort force” The effort you apply to use the machine produces the input force Output force: the force the machine exerts on the object The weight is called the “load” Generally: output force = load (weight) Also called: the “resistance force” (because it resists, or acts against, the load) The load causes the lever to pivot in one direction The output force acts to balance the load

Input Force and Output Force The input force on a body limb comes from muscles pulling on bone The distance from a fulcrum to a force is called the lever arm Each lever has a lever arm defined for the input force and another defined for the output force Contraction of the biceps exerts an input force on the lever of the forearm In the case of your forearm, the lever arm is very short, just a few centimeters from the elbow

Changing Force Size and Movement Distance A lever can change a small input force into a large output force can also change the direction of a force The farther the input force is from the fulcrum, the greater the output force will be Trade off between distance and force Apply less force to lift the rock, but must move the lever over a greater distance than the rock actually moves

Changing Force Size and Movement Distance Some levers, including many in the body, change a large input force into a small output force Trade off is between having a larger force and having a larger range of motion Like a rake! And your bicep!

Classes of Levers Depend on placement of input force, output force, and fulcrum First-class levers: the fulcrum is between the input and output forces Second-class levers: the output force is between the fulcrum and the input force Third-class levers: the input force is between the fulcrum and the output force Third-class levers always decrease the output force in favor of speed or distance I-F-O F-O-I F-I-O

Classes of Levers 1st I-F-O 2nd F-O-I 3rd F-I-O

Examples of class 2 levers include: * Wheelbarrow * Crowbar * Nut cracker Examples of class 1 levers include: * Teeter-totter * Oars on a boat * Catapult * Shoehorn * Scissors * Pair of pliers Examples of class 3 levers include: * Tweezers * Stapler * Mousetrap * Broom * Hockey stick

1st I-F-O 2nd F-O-I 3rd F-I-O

The body’s levers can be used effectively Using a lever puts stress on both the lever and the fulcrum––the bone and the joint Lifting can strain your muscles Take care of yourself! Bending over causes your back to become a lever, and puts stress on your spine Lifting with your legs uses the leg bones as levers strong muscles in your thighs and calves provide the input force

The body’s levers can be used effectively Your hand is a lever with the fulcrum at the wrist Your forearm is a lever with a fulcrum at the elbow. Your upper arm is a lever with a fulcrum at the shoulder

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