Ch. 7 notes.ppt

7/30/2019 Ch. 7 notes.ppt

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Ch. 7Forces and Motion in Two

Dimensions

Milbank High School


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Sec. 7.1Forces in Two Dimensions

Objectives Determine the force that produces equilibrium

when three forces act on an object Analyze the motion of an object on an inclined

plane with and without friction


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What is meant by two dimensions?

Consider a golf ball being hit out of a sandtrap It has a horizontal force AND a vertical force We can solve for many different things using

a combination of forces and vectors Height of the ball

Time in the air Velocity when it hits the ground


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Equilibrant

A force exerted on an object to produceequilibrium

Same magnitude as the resultant force butopposite in direction


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Solving problems in twodimensions

Draw it out! Rearrange vectors to form a triangle if

possible Solve for the resultant vector

Opposite in direction

Example Problem Pg. 151


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Sec. 7.2Projectile Motion

Objectives Recognize that the vertical and horizontal

motions of a projectile are independent Relate the height, time in the air, and the

initial velocity of a projectile using its verticalmotion, then determine the range.

Explain how the shape of the trajectory of amoving object depends upon the frame of reference from which it is observed.


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Projectiles have independentmotions!

Projectiles have two velocities, one in thex direction, and one in the y direction

x is always constant y will be changing due to the acceleration

due to gravity


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Velocity of projectiles launchedhorizontally

vx = initial velocity vy = (-g)t

v = resultant velocity vector

Example Pg. 157


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Effects of air resistance

We ignore the effects of air resistance for these problems

Sometimes it would make a largedifference, other times it wouldnt

Many projectiles modified so that theyreduce air resistance


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Projectiles launched at an Angle

Usually given angle of launch and velocity What do we have to find?

Maximum height Range

Horizontal distance

Flight time hang time


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Projectiles Launched at an Angle

Two initial velocity components vxo

vyo

How do we find these?

vx = v o(cos )vy = v o(sin )


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Projectiles Launched at an Angle

tup = v yo/g ttotal = 2(t up )

Peak Heighty = v yot - gt 2

RangeR = v xot


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Projectiles launched at an Angle

The Flight of a Ball Example Problem Pg. 159


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Sec. 7.3Circular Motion

Objectives Explain the acceleration of an object moving

in a circle at constant speed

Describe how centripetal accelerationdepends upon the objects speed and theradius of the circle

Recognize the direction of the force thatcauses centripetal acceleration

Explain how the rate of circular motion ischanged by exerting torque on it.


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Uniform Circular Motion

Movement of an object at constant speedaround a circle with a fixed radius

Merry-go-round

Circumference = 2*pi*Radius


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Vectors


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Acceleration

Which direction? Always towards

the center


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Centripetal Force

Center seeking Net force towards the center that causes

the object to try to seek the center What force is pulling it in? As a bucket of water istied to a string and spunin a circle, the force of tensionacting upon the bucket providesthe centripetal force required for circular motion.


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Net Force


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Example Problem Pg. 165

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