Download 6-1 Gravity and Motion

Chapter 6
Forces in Motion
6-1 Gravity and Motion
• Objects Falling
– All objects fall with the
same acceleration
– Gravity Constant
• 9.8 m/s2 on Earth
• To fin the Velocity of
an object you must use
this equation
• V=g*t
6-1 Gravity and Motion
• Find the Velocity of a penny that is dropped
after it falls for 2 seconds
• A rock hits the ground after falling for 4.5
seconds, what is the velocity?
6-1 Gravity and Motion
• Air Resistance
– fluid friction between
the air and the object
– slows down
acceleration
– will affect objects
differently
6-1 Gravity and Motion
• Terminal Velocity
– the point where
acceleration stops
– the upward force of air
resistance matches the
downward force of
gravity
• = a net force of 0 N
6-1 Gravity and Motion
• Free Fall
– occurs with no air
resistance
– all objects will fall at
same acceleration
6-1 Gravity and Motion
• Orbiting Objects
– are in free fall
– object moves forward
but is pulled by a larger
object
– smaller object path is
curved by gravity of
larger object
6-1 Gravity and Motion
• Orbiting Objects
– centripetal force
• unbalanced force that
causes object to move
in a circular path
• constantly changing
direction there for is
always accelerating
6-1 Gravity and Motion
• Projectile Motion
– the curved path an
object follows when
thrown or propelled
near the surface of the
Earth
– 2 Components
• Horizontal Motion
• Vertical Motion
6-1 Gravity and Motion
• Projectile Motion
– Horizontal Motion
• the motion that is
parallel to the ground
• Baseball
– once you throw the
ball there is now
more horizontal force
on the ball
– ball’s horizontal
velocity is constant
once it leaves your
hand
6-1 Gravity and Motion
• Projectile Motion
– Vertical Motion
• the motion
perpendicular to the
ground
• acts on all falling
objects
6-2 Newton’s Laws of Motion
• Newton’s First Law of
Motion (Law of Inertia)
– States that an object at rest
will remain at rest and an
object that is moving at
constant velocity will
continue moving at
constant velocity unless
acted upon by an
unbalanced force
6-2 Newton’s Laws of Motion
• Friction
– The unbalanced force
that will stop motion
– Will change the
motion of an object
in the direction of the
friction
6-2 Newton’s Laws of Motion
• Newton’s First Law of
Motion (Law of Inertia)
– Inertia
• The tendency of an
object to resist change in
its motion
• The greater the mass the
greater the inertia
• The greater the velocity
the greater the inertia
6-2 Newton’s Laws of Motion
• Newton’s Second Law of Motion
– The net force on an object is equal to the product of its
acceleration and its mass
6-2 Newton’s Laws of Motion
• Newton’s Second Law of
Motion
– Force = Mass x
Acceleration
• Unit is the Newton
(N)=kg x m/s2
– Acceleration = Force / Mass
– A 68 kg water-skier is being
pulled by a speedboat. The
force causes her to
accelerate at 2 m/s2.
Calculate the net force that
causes this acceleration.
•
•
•
•
Force = Mass x Accel
Force = 68 kg x 2 m/s2
Force = 136 kg x m/s2
Force = 136 N
6-2 Newton’s Laws of Motion
• Changes in Force and
Mass
– How to change
acceleration?
• If Force goes up accel
goes up
• If force goes down accel
goes down
• If mass goes up accel
goes down
• If mass goes down accel
goes up