Apparent WeightAcceleration of GravityForce of GravityNormal WeightFalse WeightAccelerated WeightWeightlessnessApparent WeightApparent WeightAcceleration of GravityAcceleration of GravityObjects that fall to the Earth all experience an Objects that fall to the Earth all experience an acceleration.acceleration.The acceleration due to gravity is The acceleration due to gravity is gg = 9.8 m/s = 9.8 m/s22..This acceleration must be due to a force. This acceleration must be due to a force.Force of GravityForce of GravityThe acceleration of a falling The acceleration of a falling mass mass mm is - is -gg..The force on the mass is The force on the mass is found from found from FF = = mama (action). (action).This gravitational force is This gravitational force is FF = - = -mgmg..gaKinematic viewgmFgravDynamic viewNormal WeightNormal WeightWe measure weight with a scale We measure weight with a scale that measures normal force.that measures normal force.•WW = = mgmgWeight is related to mass by the Weight is related to mass by the gravitational field gravitational field gg..False WeightFalse WeightA vertical acceleration can A vertical acceleration can change the weight.change the weight.The normal force on the floor The normal force on the floor is our sense of weight.is our sense of weight.•Downward acceleration Downward acceleration reduces weightreduces weight•Upward acceleration Upward acceleration increases weightincreases weightMass is unchanged.Mass is unchanged.Newton’s law of accelerationNewton’s law of accelerationFF = = mamanet force, net force, FF = - = -mgmg + + FFNN..Solve for the normal forceSolve for the normal force--mgmg + + FFNN = ma = maFFNN = = mama + + mgmgFFNN = = mm ( (aa + + gg))Apparent mass based on Apparent mass based on ggmmappapp = = FFNN / / ggAccelerated WeightAccelerated WeightAn elevator is accelerating An elevator is accelerating downward at 2.0 m/sdownward at 2.0 m/s22..The person has a mass of The person has a mass of 70 kg. 70 kg. What mass is on the scale?What mass is on the scale?Add all the forces, but the Add all the forces, but the net force is –net force is –mama = = FFNN – – mgmg..Solve for Solve for FFNN = = m m ((gg – – aa))Convert to mass Convert to mass mmappapp = = FFNN / /ggThe scale shows 56 kg.The scale shows 56 kg.WeightlessnessWeightlessnessIf the elevator accelerated downward at If the elevator accelerated downward at gg, the normal , the normal force would become 0.force would become 0.•FFNN = = m m ((gg – – aa) = ) = m m ((gg – – gg) = 0) = 0The person would feel weightless.The person would feel weightless.An object in free fall is weightless, but not massless.An object in free fall is weightless, but not massless.nextMicrogravity research at
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