Sph4c Chapter 2 Simple Machines LoRusso

Transcription

1 Sph4c Chapter Simple Machines orusso Machine: A machine is any evice that helps us perform a task. hey are esigne to achieve at least one of five main functions Change energy from one form to another. (i.e. win energy into electricity, chemical energy such as gasoline into kiic energy, the energy of motion like when you rive a car) ransfers energy..g. the chain of a bike transfers energy from your legs to your wheels Change the irection of a force..g. pulling own on a curtain chor will raise a curtain Change a magnitue of force..g. Using a tire iron to loosen the lug nuts on a tire. he longer the iron, the greater the force Change the istance or spee..g. he gear system of a bicycle, the higher the gear, the slower your legs have to turn in orer to maintain the same spee Simply Machines: A simple machine is a evice that performs one simple task. Simply machines are broken into the two categories he lever family incluing evice such as lever pulley wheel axle gears he incline plane family incluing evices such as incline plane wege screw he ever amily evers are a rigi bar the rotate about a point calle a fulcrum he effort force ( ) is the force applie to one part a lever in orer to exert a force on a loa on the other part of the machine he loa force ( ) is the force the loa applies to the lever he effort force is applie to the effort arm that is measure between the point where the effort force is applie an the fulcrum ( ) he loa force is applie to the loa arm that is measure between the point where the loa force is applie an fulcrum ( )

2 Sph4c Chapter Simple Machines orusso Other types of levers Biomechanical systems: Arms, legs, jaws, beaks etc. Pulley: A wheel with a groove rim, rotating about a central fulcrum..g. rope-pulley or belt-pulley, such as what is foun in the engine of a car. Wheel an axle: large-iameter, rigi circular isk (the wheel) connecte to a small-iameter, rigi ro (the axle). Both wheel an axle rotate about the same fulcrum.

3 Sph4c Chapter Simple Machines orusso Gear: oothe wheels of ifferent iameters, linke together to increase or ecrease spee or to change irection. Gears rotate about the same fulcrum therefore are similar to wheels. Incline Plane amily of Machines Incline planes reuce effort by: Increasing the istance of the effort force. Ramp ( a single incline plane) Concentrating the effort force Wege (a ouble incline plane) Screw (an incline plane wrappe aroun a central shaft) he car jack is consiere a compoun machine because it consists of two or more simple machines. i.e. levers (the jack part), wheel an axle (the hanle an screw part) orque an evers orque is the turning effect achieve when using a rigi boy such as a lever to rotate about a central axis.

4 Sph4c Chapter Simple Machines orusso orque epens on two things. he effort force ( - this means orque is proportional to orce or as orce increases orque increases). he istances between effort force an the rotating axis ( ) ormula: = or = Where is torque in N m (Newton-meters), is force in N (Newtons) an is in m (meters) Note: we are assuming that the applie force is perpenicular to the lever. If the force is not perpenicular, we woul have to use a more complicate formula. However, for our purposes, the above formula is sufficient. Direction: orques are technically vectors, meaning that they have irection here are the rules. CCW (counter clockwise) orques = +. CW (clockwise) orques = - Net orque: Just like force, if the torque is zero ( = 0N m or rotate at a constant angular velocity. If r r r = system combine xample: consier the following system that s in equilibrium. ) then the system will NO rotate = 0 N m then the system is sai to be in equilibrium. this means that the torque is the sum of all the torques acting on the et be the loa on the left an let be the loa on the right Since woul cause the system to want to rotate counter clockwise about the fulcrum the is positive Since woul cause the system to want to rotate clockwise about the fulcrum the is negative. r r r = + = = = ( 5.0)(.0) (.0)(.5) = = 0N m

5 Sph4c Chapter Simple Machines orusso In General fulcrum Where is the effort torque in N m (Newton-meters), is the loa torque in N m (Newton-meters), is the effort force in N (Newtons), is the loa force in N (Newtons), is the length of the effort arm in m (meters), an is the length of the loa arm in m (meters) = OR = AND =