Download Forces and Motion

Physics Flipped Notes
Take notes on this powerpoint in
your journal. Title your journal:
Forces and Motion
Forces and Motion
Demonstrate and calculate how
unbalanced forces change the speed
or direction of an objects motion
Force
• Any push or pull on an object
• Acts in pairs
• Measured in Newtons (N)
• Every force has a magnitude and direction
• Forces can work together or against each other
• Forces can be balanced or unbalanced
Vectors
• Lines with arrows that show direction and
magnitude of a force.
• Length of the line shows the amount of force
(magnitude)
• The arrow shows the direction of the force.
Balanced Forces
• Do not cause a change in motion
• Occurs when objects are at rest or traveling at a
constant speed and direction.
Balanced forces
Unbalanced Forces
• Always cause a change in motion
• Occurs when there is a change in speed or
direction of motion
Net Force
• Combination of all forces acting on an
object.
– Add forces working in the same direction.
2N
Net Force: 8 + 2 = 10 N
8N
– Subtract forces that are working in opposite
directions.
7N
3N
Net Force: 7 – 3 = 4 N
Add forces acting in the
same direction
Example:
8 N + 6 N = 14 Newtons
Subtract forces acting in
opposite directions
Example:
20 N – 18 N = 2 Newtons
Net Force = 0
Forces are balanced
Example:
20 N – 20 N = 0 Newtons
• Forces are balanced - No change in motion
Newton’s 1st Law of Motion
States that:
• An object at rest will stay at rest unless
acted on by an unbalanced force.
And:
• An object in motion will stay in motion at
the same speed and direction unless
acted on by an unbalanced force.
In other words…
• An object will keep doing what it is doing unless
forces become unbalanced
• Also known as the “Law of Inertia”
• Inertia – An object’s tendency to resist change
Law of Inertia (1st law)
Newton’s 2nd Law of Motion
• The acceleration of an object by a force is
inversely proportional to the mass of the object
and directly proportional to the force applied.
In other words…
• The smaller the object, the greater the
acceleration AND the larger the object, the
smaller the acceleration.
• The smaller the force applied, the smaller the
acceleration AND the larger the force applied
the larger the acceleration.
Therefore…
Force = Mass X Acceleration; F = ma
Example: Force = 1,000 kg X .05 m/s/s
Force = 50 Newtons
Newton’s 3rd Law of Motion
• For every action, there is an equal but
opposite reaction
In other words…
• All forces act in pairs.
• When one object exerts a force on a second
object, the second object exerts a force back
that is equal in size but opposite in direction
Newton’s 3rd Law
Space Shuttle Launch
Example: Action-Reaction
Speed
• How fast an object is moving
• Rate at which an object covers a distance
• Speed = distance ÷ time
Example: Calculating Speed
While on vacation, Lisa Carr traveled a total
distance of 440 miles. Her trip took her 8
hours. What was her average speed?
• Speed = distance ÷ time
• Speed = 440 miles ÷ 8 hours
• Average speed = 55 miles/hour
What’s the difference between
Speed and Velocity?
• Velocity - The rate at which an object
changes position. It’s the measurement of
the rate and direction of motion.
Work
• Occurs when a force is used to move an
object through a distance
• Measured in Joules(J) = Newtons/meter
• Work = Force (N) X Distance (m); W = Fd
• How much work is done if a force of 20N is
used to displace an object 3m?
• Work = (20N) X (3m)
• Work = 60 Joules (J)
THE END