1 Newton’s Laws 2 1 st Law – Inertia Newton's first law of motion is often stated as: An object at rest tends to stay at rest and an object in motion.

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Newton’s LawsNewton’s Laws

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11stst Law – Inertia Law – Inertia

• Newton's first law of motion is often stated as:

• An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.  

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22ndnd Law Law

• Newton's second law of motion can be formally stated as follows:

• The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. In terms of an equation, the net force is equated to the product of the mass times the acceleration.

• Fnet = m a

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33rdrd Law Law

• "For every action, there is an equal and opposite reaction."

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11stst law restated law restated

• Inertia - the tendency of an object to resist a change in its motion– If at rest, wants to stay at rest– If moving, wants to continue moving– UNLESS ACTED UPON BY AN OUTSIDE

FORCE!– http://www.glenbrook.k12.il.us/gbssci/phys/

Class/newtlaws/u2l2b.html

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Inertia and mass are related in that

the more massive an object is

the more resistance to change in

the object’s motion

or

INERTIA

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AssignmentsAssignments

• On Slide 8 do: 1-6

• On Slides 9 - 12 do: 1-9, 12, 13-21 (odds only), 36. Show formulae, work with numbers and units, and answers with numbers and units for 13-21 odds.

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There are many more applications of Newton's first law of motion. Several applications are listed

below – try to provide explanations for each

application.

• blood rushes from your head to your feet when riding on a descending elevator which suddenly stops.

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•the head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface.

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a brick is painlessly broken over the chest of a physics teacher by slamming the brick with a sledge hammer. (CAUTION: Do not attempt this at home!)

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to dislodge ketchup from the bottom of a ketchup bottle, the bottle is often turned upside down, thrust downward at a high speed and then abruptly halted.

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headrests are placed in cars to prevent whiplash injuries during rear-end collisions.

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while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb, a rock or another object which abruptly halts the motion of the skateboard.

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2nd Law (F=ma)

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F

m a

Force, F units: newtons 2nd LawMass, m kg

Acceleration, a m/s 2

Problem:

Find the net force necessary for a

l.6 x 103 kg car to accelerate forward at 2.0 m/s2.

F = ma = 1.6 x 103 kg (2.0 m/s2)

F = 3.2 x 103 kgm/s2 or newton, n

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Weight = mass x free fall acceleration

• W = mg

• On Earth, g = 9.8 m/s2

• A 1.0 kg object has a weight of l.0 kg x 9.8 m/s2 = 9.8 n

If you weigh 125 lb, find your weight in newtons.

125 lb 1 kg 9.8 m = 556.8 n

2.2 lb s 2

What law is this?

w

m g

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3rd Law

For every action forceThere is an equal and opposite

reactionforce.

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ETC.

• Centripetal Force - the force that pulls an object moving in a circle toward the center of the circle.

Object moving clockwise in a circle is always being pulled toward the center of the circle.

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2.

1. and 2. show centripetal force vectors.

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Kinetic and Potential Energies

• Kinetic Energy - energy of motion

• Potential Energy - energy of position

KE = max

PE = 0

KE = 0PE = max

KE = 0PE = max

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KE and PE

• KE = ½ m v2

Kgm2 = joule or j

v2

• PE = mgh Kg m m = joule also

s2

g = 9.8 m/s2

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12.4 Universal Forces

• Electromagnetic Forces - act between charged particles– Opposites attract for both electric and magnetic forces– Electric force is responsible for repulsion of like charged

particles

• Nuclear Forces– Strong nuclear force holds neutrons and protons together in the

nucleus– Weak nuclear force (weaker than the strong n.f.) acts only over

very small distances and is involved in nuclear decay

• Gravitational - acts between any two objects in the universe and acts over large distances