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# Weight - PowerPoint PPT Presentation

Weight Acceleration of Gravity Objects that fall to the Earth all experience an acceleration. The acceleration due to gravity is g = 9.8 m/s 2 . This acceleration must be due to a force. The acceleration of a falling mass m is - g .

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## PowerPoint Slideshow about 'Weight' - libitha

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### Weight

• Objects that fall to the Earth all experience an acceleration.

• The acceleration due to gravity is g = 9.8 m/s2.

• This acceleration must be due to a force.

The force on the mass is found from F = ma (action).

This gravitational force is F = -mg.

Force of Gravity

Kinematic view

Dynamic view

• The force of gravity acts on all objects all the time.

• If an object is at rest, the law of inertia says that the net force is zero.

• There must be a force opposite to gravity that cancels it out.

F = -Fgrav =mg

Fgrav = -mg

• The force that opposes gravity for objects on the ground is called the normal force.

• It is perpendicular (normal) to the plane of the ground.

• The force is a result of the law of reaction.

FN = mg

Fsb = -Fbs =mg

• The normal force pushing up against gravity can be measured.

• We measure weight with a scale that measures normal force.

• Weight is a force, not a mass.

• Pounds measure weight, so force (not mass) can be measured in pounds.

• An elevator is accelerating downward at 2.0 m/s2.

• The person has a mass of 70 kg.

• What weight is on the scale?

• Add all the forces, but the net force is –ma = FN – mg.

• Solve for FN = m (g – a)

• The scale shows 56 kg.

• If the elevator accelerated downward at g, the normal force would become 0.

• The person would feel weightless.

• An object in free fall is weightless, but not massless.

Microgravity research at NASA

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