Transcript The student will demonstrate an understanding of motion, forces

Physics Basics
TAKS Objective Four
TAKS Objective 4 – The student will
demonstrate an understanding of motion,
forces, and energy.
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.
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.
True or False
• Speed is the same as velocity.
• False.
True or False
• The acceleration of an object does NOT
depend on its mass.
• False.
True or False
• An ice skater uses projectile motion.
• False
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
Projectile Motion
Consider two-dimensional motion:
A horizontal motion that follows Newton’s 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 Newton’s Second Law (F = ma).
Example of Projectile Motion
Newton’s 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.
Newton’s Second Law
• The acceleration of an object depends on
the force applied to the object and the
mass of the object. F = ma
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
Two types of forces
• Contact Force
– normal, frictional,
tensional, and applied
forces
• Action-at-a-distance
interaction forces
– gravitational, electrical,
and magnetic forces
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 6kg object?
• 4m/s2 and 2m/s2
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
Newton’s 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.
Definitions
• Speed – describes an object’s change in
position over time
– Speed = Distance / Time
Definitions
• Velocity – the speed AND direction of an
object. Velocity= Distance / Time plus
direction. Example: 3 m/s eastward
Definitions
• Acceleration – a change in either the
speed or the direction of an object.
= Force / Mass
• Which car(s) is/are accelerating?
A
Which letter represents which
car?
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
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.
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
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.