I. Motion – an objects change in position over time when compared

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Transcript I. Motion – an objects change in position over time when compared

I. Motion – an objects change
in position over time when
compared to a reference
A. Reference point- an object
that appears to stay in place;
building, trees, etc.
Distance and displacement
B. Distance- the length that is traveled
C. Displacement- the distance between
the starting and ending points.
D. Speed- the rate at which an
object moves; depends on the
distance traveled and the time
taken to travel that distance.
Speed = distance
Calculate speed:
• If you walk for 1.5 hours and travel 7.5 km,
what is your average speed?
• What is your average speed if you take 0.5
hour to walk 4000m?
Solving speed using the triangle:
Example: If the average speed of a car is
110 km/h, how long will it take the car to
travel 715km?
E. Velocity-the speed of an object in
a particular direction; velocity
always includes a direction (N,
S, E or W, upward, downward)
Velocity = distance / time
A direction is always given.
• 1. Resultant Velocity – velocity that
results when two directions are
traveled at once.
Ex. A bus travels 15 m/s east. A
passenger on the bus walks toward
the front of the bus at a speed of 1
m/s. Find the resultant velocity.
Example 2: A bus travels 15 m/s while
a passenger on the bus moves to the
back of the bus at a speed of 1 m/s.
Find the resultant velocity.
F. Acceleration- the rate at which
velocity changes; this can be both
positive (speeding up) or negative
(slowing down) or simply changing
Acceleration = final velocity - initial velocity
Example: A plane passes over Point A with
a velocity of 8000 m/s N. Forty seconds
later it passes over Point B at a velocity of
10,000 m/s N. What is the plane’s
acceleration from A to B?
Example 2: A coconut falls from the
top of a tree and reaches a velocity of
19.6 m/s when it hits the ground. It
takes 2 seconds to reach the ground.
What is the coconut’s acceleration?
1.Centripetal acceleration- the
acceleration that occurs in circular
motion; windmill blades, ferris wheels, roller
coasters with loops, jugglers
G. Inertia- the tendency of an object to
resist change; you keep moving forward
after the car stops. The inertia of an
object increases as mass increases.
H. Momentum- a measure of how hard it is
to stop an object; depends on mass and
I. Law of Conservation of Momentum- the
total momentum of a group of objects
remains constant unless outside forces act
on the group; friction slows down balls on
a pool table
II. Force- a push or a pull
A. Newton- SI unit of force
B. Examples of forcespushing an object, pulling an object,
gravity, weight, friction
1. Net force- the force that
results from combining all the forces
exerted on an object.
C. Balanced forces- forces on an
object that cause the net force to be
zero. Balanced forces do not cause
a change in motion or acceleration.
(The push is equal to the pull; both
sides of the seesaw are equal)
D. Unbalanced forces- forces on an
object that cause the net force to be
other than zero; unbalanced forces
produce a change in motion or
E. Gravity- force of attraction between
two objects that is due to their
masses and the distance between
the objects. (Law of Universal
1. Gravitational force increases as
mass increases
2. Gravitational force decreases
as distance increases.
F. Weight- a measure of the
gravitational force exerted on an
object. Weight is a force and is
measured in newtons.
1. mass- the amount of matter in an
object; this remains unchanged no
matter how much gravity is exerted
on an object.
• G. Friction- force that opposes
motion between two surfaces that are
H. Types of friction:
1. sliding friction- friction that
occurs as an object slides across
another object; brakes applied on a
car, writing with chalk, etc.
2. rolling friction- friction on an
object that has wheels in motion
3. fluid friction- friction between
water and an object
4. static friction- a force applied to
an object but does not cause the
object to move
I. Reducing friction
1. Lubricants- reduces the
friction between them; motor oil, wax
and grease
2. Smoother surfaces
J. Increasing friction- rougher
surfaces (a tire with tread is better for
stopping than a bald tire)
Newton’s 3 Laws of Motion
J. Newton’s 1st Law of Motion- states that
an object at rest will remain at rest unless
reacted upon by an unbalanced force and
an object in motion will remain in motion
unless reacted upon by an unbalanced
• K. Newton’s 2nd law of Motion- states that
force = mass X acceleration
L. Newton’s 3rd law of Motion- states that
for every action force there is an equal and
opposite reaction force