Introducing 

Prezi AI.

Your new presentation assistant.

Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.

Loading…
Transcript

CH 10

Motion and Forces

Physical Science

10.1 Intro to Motion

1. What is the study of matter and energy and the interactions occuring between them?

2. What are the 2 components of a vector quantity?

3. Define distance and displacement

10.1

4. What term describes a cector showing the combined effec of 2 or more vectors

5. Define mechanics

6. Contrast speed and velocity

7. What term refers to any change in velocity?

8. What term describes a decrease in velocity over times?

Path to Modern Physics

Path to Modern Physics

  • Physics- the study of matter and energy and the interactions occurring between them.
  • Began with Greek philosophers and Aristotle. They however rarely checked their ideas experimentally, so many of their assumptions have been proven false or incorrect
  • Galileo and Isaac Newton founded modern physics .
  • Galileo viewed the universe, the world, and living things as the special creation of God
  • Sir Isaac Newton was greatly influenced by Galileo's work. He discovered the laws of motion and gravitation.
  • Modern physics- quantum mechanics, relativity, solid-state physics, and particle physics
  • Classical physics- branches of physics developed before 1900; mechanics, thermodynamics, optics, acoustics, and electromagnetism.

Scalars and Vectors

Scalars and Vectors

  • Scalar quantity- has only magnitude(size or amount)
  • Vector quantity- both magnitude and direction; represented by arrows with the length symbolizing magnitude and the direction the arrow points being direction.

Distance and Displacement

  • Distance- a scalar representing the total length of the object's path
  • Depends on the object's path
  • Displacement- object's change in position
  • Mathematically: displacement=final position- initial position
  • ∆x = xf - xi
  • Depends only on the final and initial positions, not the path taken
  • Vector having both magnitude and direction
  • The magnitude of displacement equals the straight-line distance between the starting and ending position, without regard to direction.
  • Distance and displacement in 2D
  • Distance is still the total length of the object's path
  • Displacement- the change in the object's position

Vector Addition

  • Vector Addition- 2 different vectors combined
  • Resultant- the answer of vector addition; a vector showing the combined effect of 2 or more other vectors
  • Is a new vector and should be given both a magnitude and direction
  • Collinear- vectors that are in the same direction or in opposite directions; in 1D
  • Can be represented by signed numbers.
  • To add the vectors add the signed numbers
  • Perpendicular vectors
  • Magnitude of the resultant can be found by using the Pythagorean Theorem

Describing Motion

Describing Motion

  • Motion- objects changing position
  • Dynamics- the study of motion and forces
  • Mechanics- the branch of physics that addresses the effects of forces on matter
  • 3 terms in describing motion:
  • Speed- the distance traveled by an object per unit of time; measures how quickly an object moves; scalar
  • s= d/t
  • Instantaneous speed- the speed of a moving object at any given instant
  • Average speed- speed calculated over a distance
  • Velocity- the displacement of an object per unit of time; vector
  • v= ∆x/t
  • Acceleration- any change in velocity
  • Occurs when a moving object experiences a change in either speed or direction (or both)
  • Average acceleration- the change in velocity per unit of time
  • a= ∆v/t
  • Deceleration- negative acceleration; when something slows down.

Newton's Laws of Motion

10.2

1. In what book did Sir Isaac Newton publish his laws of motion?

2. State Newton's first law of motion.

3. According to Newton's 2nd law of motion, how is the magnitude of the force applied to an object related to the object's acceleration? To the object's mass?

4. State Newton's 2rd law of motion.

1st Law

1st Law

  • Sir Isaac Newton- presented his findings to the world in his book Principia where he proposed the 3 basic laws of motion applying to all objects
  • First law of motion- an object at rest stays at rest, an object in motion stays in motion
  • the velocity of an object does not change unless the object is acted upon by an external force
  • Inertia- the tendency of matter to resist change
  • This law is also considered the law of inertia

2nd Law

2nd Law

  • Second law of motion- the force required to accelerate an object at a certain rate equals the object's mass times the desired acceleration
  • F=ma
  • Is also the definition of N the SI unit for force
  • The force applied to an object is directly proportional to its acceleration
  • The force required to accelerate an object is also proportional to the object's mass

3rd Law

3rd Law

  • Third law of motion- for every action there is an equal and opposite reaction
  • When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

Forces in Nature

1. According to the law of universal gravitation, how is the force of attraction between two objects affected if the mass of either object increases? How is the force affected if hte distance is doubled

2. Expalin what the equation Fw=mg means.

3. What force causes an object to travel in a curve rather than in a straight line?

4. Name the two fundamental causes of friction.'

5. Compare and contrast kinetic and static friction.

6. Upon what two things does friction depend?

10.3

Force of Gravity

Force of Gravity

  • Law of universal gravitation- any 2 objects attract each other through gravitational force.
  • F=G (m1m2/d^2)
  • G- gravitational constant;
  • An object that is dropped accelerates toward the ground due to gravity, the gravitational force exerted on an object near the surface of the earth or any celestial body.
  • Free fall- fall with no effect from forces other than gravity; all objects near the earth's surface accelerate at the same rate.
  • Acceleration of gravity- a falling object will add 9.81 m/s to its speed every second it falls
  • d=1/2(g)(t^2)
  • Terminal velocity- when an object reaches a velocity at which the force of the drag equals the object's weight.
  • Fw=mg

Solids in Circular Motion

Solids in Circular Motion

  • Centripetal force- causes the object to travel in a curved path rather than a straight line.
  • Centrifugal force- a pull created by an object’s inertia causing it to curve rather than travel in a straight line.
  • The result of the weight’s attempt to move in a straight line; it can be considered the reaction force of centripetal force

Friction

Friction

  • Friction- unseen force; resistance arising to an object’s motion through a fluid or across a surface
  • Causes
  • Attraction- common in metals; molecules in 2 surfaces close together attract each other and form temporary weak bonds causing them to stick together
  • Ex; piece of tape to a paper
  • Repulsion- microscopic irregularities in the sliding surfaces; stopping movement; negatively charged electrons in adjacent atoms repel preventing two atoms from occupying the same space.
  • Ex: sandpaper
  • Types
  • Kinetic friction- affects sliding objects already in motion; it remains constant and acts to slow objects down
  • Static friction- affects stationary objects, preventing them from moving at all
  • Rolling friction- affects rolling objects

  • Forces of friction
  • Friction depends only on the weight of the object and the nature of the surfaces in contact
  • Coefficients of friction- unitless values that express the effect of the surfaces; symbolized by the lowercase Greek letter μ
  • Kinetic friction force: Fkf= μkFw

Work, Power, and Momentum

1. Define work.

2. What is the SI unit of work and energy?

3. Define power.

4. What is the product of an ojbect's mass and velocity?

5. State the law of conservation of momentum.

10.4

Work

Work

  • Work- the transfer of energy from one object to another by a force; done only when an object is moved
  • W=Fd
  • The amount of work done equals the amount of energy transferred.
  • Measured in J; one J equals the work performed by 1 N force over a distance of 1 m

Power

Power

  • Power- the rate of doing work, or work per unit of time
  • P= W/t
  • Power is directly related to work; doing a greater amount of work in a given amount of time requires more power
  • Power is inversely related to time; the more time it takes to do a certain amount of work, the less power is used and vice versa
  • Units is watts (W)

Momentum

Momentum

  • Momentum- quantity of motion; the product of the object's mass and velocity
  • p=mv
  • Expressed in units (kg*m)/s
  • Directly related to mass
  • Momentum is a product of a scalar and a vector it is a vector with the same direction as velocity
  • Two equal and opposite momenta cancel each other out
  • The momentum of an object is constant(conserved) unless an outside force acts upon the object
  • Law of conservation of momentums- the overall external force acting on a system is 0, the momentum of the whole system remains constant.
  • Momentum is not the same thing as kinetic energy

Simple Machines

1.What is ideal mechanical advantage? How is it different from actual mechanical advantage?

2. Which is greater under ordinary conditions, work input or work output?

3. Why can no machine be 100% efficient?

4. Name the pivot point upon which the beam of a lever rests.

5. Which simple machine can be considered a circular lever?

6. What type of machine combines fixed and movable pulleys?

7. Which simple machine consists of a sloping platform that enables an object to be raised without lifting it straight up.

8. What simple machine can be visualized as an inclined plane wrapped around a rod?

10.5

Machine Terminology

Machine Terminology

  • Machines- devices for doing work
  • Simple Machines- early force multiplying machines
  • Provide 3 forms of assistance
  • Multiply the applied force
  • Multiply the distance the applied force moves something
  • They can change the direction of the force
  • Input- force applied to the machine
  • Work input: Wi=Fidi
  • Output- input force modified
  • Work output: Wo=Fodo
  • Under ideal conditions the work put into a machine is equal to the work received from the machine

  • Mechanical advantage- the number of times a machine multiplies input
  • Ideal mechanical advantage(IMA)- the mechanical advantage under ideal conditions
  • IMA= input distance/ output distance
  • Actual mechanical advantage(AMA)- the multiplication of input force that a machine provides
  • AMA= output force/ input force
  • Efficiency- the ratio of work output to work input
  • η= Wo/Wi

6 Simple Machines

6 Simple Machines

  • Lever- multiply force or speed with or without changing the input direction
  • Fulcrum- pivot upon which the beam rests
  • Classified according to where the input and output forces are in realtion to the fulcrum.
  • Class 1- in input an output forces are on opposite sides of the fulcrum
  • Has an input arm and output arm
  • If the input arm is longer than the output arm , the force is multiplied ; if the input arm is shorter than the output arm, speed is multiplied instead.
  • Class 2- fulcrum is at one end of the lever, the input it applied at the other end, and the output is between the input and the fulcrum
  • Input and output arms overlap and direction of the input is not changed.
  • Class 3- fulcrum at one end of the lever, the output at the other end, and the input force applied between the fulcrum and the output; direction of force does not change
  • Ideal mechanical advantage of lever: IMA= input arm/output arm
  • Wheel and axle- depending on where the input and output are applied, the wheel and axle multiplies either force or speed but never alters the direction of the force
  • Similar to a circular lever:
  • Axis corresponds to the fulcrum
  • The axel and large wheel correspond to the arms
  • Ideal mechanical advantage: IMA= input radius/ output radius
  • Pulley- consists of a wheel over which a rope or cable passes
  • 3 main arrangements
  • Fixed pulley- a pulley that does not move with the load; both input and output forces and the input and output distances are equal
  • Movable pulley- a pulley directly attached to a moving load; allows input force applied to be only half of the output force
  • Block and tackle- a combination of one or more fixed pulleys and one or more movable pulleys; the movable pulleys multiply the input force while the fixed pulleys change its direction.

  • Inclined plane- a sloping surface that allows an object to be raised without lifting it straight up
  • Allows an object to be moved along its surface with a smaller force than would be required to directly lift the object.
  • Ideal mechanical advantage: IMA= length/height
  • Wedge- special form of inclined plane that modifies the applied force and directs it to the side.
  • Lond slender wedges require less input force to generate the same output as short, thick ones.
  • Ideal mechanical advantage: IMA=length/thickness
  • Screw- simple machine resembling an inclined plane wrapped around a rod; as it is turned, a screw applies force along its axis
  • Allow an input force exerted over a long distance to move the output a very short distance.
  • The output distance equals the pitch of the screw, the distance from one of the ridges or threads on the screw's shaft to the next.
  • IMA= 2(pie) (r) /p
Learn more about creating dynamic, engaging presentations with Prezi