Physics Basics

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Physics Basics
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TAKS Objective Four

• TAKS Objective 4 The student will demonstrate
  an understanding of motion, forces, and energy.

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Learning Objectives During this Unit

• You will apply the laws of motion to real world
  examples.
• You will identify size and direction of a force.
• You will determine if motion is constant or
  accelerated.

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Learning Objectives

• You will use equipment to measure time and
  distance so that the motion of the object can be
  determined.
• You will used data collected to calculate the
  speed of an object.
• You will explain the results of applying a force
  to an object.

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True or False

• Speed is the same as velocity.
• False.

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True or False

• The acceleration of an object does NOT depend on
  its mass.
• False.

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True or False

• An ice skater uses projectile motion.
• False

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Types of Motion

• One dimensional motion happens when only one
  directional force causes an object to move
  forward, backward, up and down, or side to side.
• Examples bowling, skiing, writing, brushing your
  teeth, painting a wall

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Projectile Motion

• Consider two-dimensional motion
• A horizontal motion that follows Newtons First
  Law.
• A vertical motion due to the force of gravity
  pulling the ball back to Earth. This is an
  acceleration motion. It is acted upon by the
  constant force of gravity and follows Newtons
  Second Law (F ma).

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Example of Projectile Motion
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Newtons First Law

• An object at rest will remain at rest and an
  object in motion will remain in motion in a
  straight line until a force opposes it.

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Newtons Second Law

• The acceleration of an object depends on the
  force applied to the object and the mass of the
  object. F ma

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Definitions

• Force A force is an interaction with an object
  which may or may not result in motion.
• Person sitting in chair
• Pushing on a wall
• Blowing a feather
• Kicking a ball

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Two types of forces

• Contact Force
• normal, frictional, tensional, and applied forces
  

• Action-at-a-distance interaction forces
• gravitational, electrical, and magnetic forces

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Force Unit defined

• One Newton is defined as the amount of force
  required to give a 1-kg mass an acceleration of 1
  m/s2.
• What acceleration will result when a 12-N net
  force is applied to a 3-kg object? A 6-kg object?
  
• 4m/s2 and 2m/s2

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F ma

• A net force of 16 N causes a mass to accelerate
  at the rate of 5 m/s2. Determine the mass.
• Write what you know. 16 m5
• 3.2 kg

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Newtons Third Law

• For every action there is an equal in size and
  opposite in direction action.

Forces always come in pairs equal and opposite
action-reaction force pairs.
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Definitions

• Speed describes an objects change in position
  over time
• Speed Distance / Time

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Definitions

• Velocity the speed AND direction of an object.
  Velocity Distance / Time plus direction.
  Example 3 m/s eastward

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Definitions

• Acceleration a change in either the speed or
  the direction of an object. A Force
  / Mass
• Which car(s) is/are accelerating?

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Which letter represents which car?
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Definitions

• Work force acting upon an object multiplied by
  the distance the object moves. (force and
  displacement must move in the same direction. W
  F X D
• Power The amount of time it takes to do work.
  Power Work / Time

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Is this work or not?

• A teacher applies a force to a wall and becomes
  exhausted.
• No, the wall did not move in the same direction
  as the force.
• A book falls off a table and free falls to the
  ground.
• Yes, gravity pulls the book downward.

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Is this work or not?

• A waiter carries a tray full of meals above his
  head by one arm across the room.
• No, his tray is moving horizontally while he is
  applying a vertical force.
• A rocket accelerates through space.
• No, the rocket engine propels the rocket in the
  opposite direction it goes.
• Joule is the unit used for work

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Study these

• Newtons Laws of Motion
• Force
• Acceleration
• Velocity
• Speed
• Work
• Joule
• Newton

• Projectile Motion
• Power
• Know how acceleration is affected by mass and
  amount of force
• Get some objects out while you study to help you
  understand what you are learning.