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Chapter 3 Section 1

Newtons Second Law

How does the mass of an object affect

how fast they can move and why dosome objects keep moving while

others stop?

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Force, Mass, and Acceleration

jThe acceleration of an object depends

on its mass as well as the force exerted

on it.jForce, mass and acceleration are

connected.

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Newtons Second Law

jNewtons second law of motion

describes how force, mass and

acceleration are connected.jAccording to Newtons second law of

motion, the net force acting on an

object causes the object to accelerate inthe direction of the net force.

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Newtons Second Law

jThe acceleration of an object is

determined by the size of the net force

and the mass of the object according tothe equation.

jAcceleration= net force/ mass

j a=F/m

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Friction

jWhat happens to the motion of a

skateboard after it leaves your hands?

jThe skateboard gradually slows downand finally stops.

jThe force that slows the skateboard

and brings it to a stop is friction.

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Friction

jFriction is the force that opposes motion

between two surfaces that are touching each

other.jThe amount of friction between two

surfaces depends on 2 factors.

The kinds of surfaces.

The force pressing the surfaces together.

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Friction

jFriction is due to microwelds formed

between 2 surfaces.

jThe larger the force pushing the 2surfaces together, the stronger the

microwelds will be.

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Friction

jIf the acceleration is zero, then the net

force of the object is zero.

jStatic friction is the friction betweentwo surfaces that are not moving past

each other.

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Friction

jAs a box slides across the floor another

force- sliding friction- opposes the motion

of the box.

jSliding friction is the force that opposes the

motion of 2 surfaces sliding past each other.

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Friction

jSliding friction is caused by

microwelds constantly breaking

and then forming again as the boxslides along the floor.

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Friction

jThe friction between a rolling object and thesurface it rolls on is rolling friction.

jThe wheels of the train rotate when theycome in contact with the track rather thansliding over it.

jRolling friction is usually much less than

static or sliding friction.jThis is why its easier to pull a load in a

wagon rather than drag it on the ground.

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Air Resistance

jAn object falls toward Earth, it is pulled

downward by the force of gravity.

jAnother force called air resistance acts onobjects that fall through the air.

jAir resistance affects anything that moves

in Earths atmosphere.

jLike friction, air resistance act in the

direction opposite the objects motion.

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Air Resistance

jThe amount of air resistance on an object

depends on the speed, size, and shape of the

object.

j If no air resistance is present, then a feather

and an apple fall at the same rate.

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Terminal Velocity

jThe force of air resistance increases with

speed.

jAs an object falls, it accelerates and itsspeed increases.

jThe force of air resistance increases until it

becomes large enough to cancel the force of

gravity.

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Terminal Velocity

jThen the forces on the falling

object are balanced, and the object

no longer accelerates.

jIt then falls with a constant speed

called the terminal velocity.