Motion and Force. Frame of Reference Motion of an object in relation to a fixed body or place. To...
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Transcript of Motion and Force. Frame of Reference Motion of an object in relation to a fixed body or place. To...
Frame of ReferenceMotion of an object in relation to a fixed body
or place.To describe motion accurately and
completelyTHE MOST COMMON FRAME OF
REFERENCE: The Earth
Relative MotionIs the movement in relation to a frame of
referenceExample:
A train going past a platform (see movement)
People riding the train feel no movement
Measuring DisplacementDisplacement—the
direction from the starting point and the length of a straight line from the starting point to the ending pointInvolves distance
and direction
Combining DisplacementVector—is a quantity that has magnitude and
directionAdd displacements using vector addition
If vectors are in the same directions, add them Ex:
10meters 5 meters = 15 meters
If vectors are in the opposite direction, subtract themEx:
20 meters 15 meters = 5 meters
Resultant vector—the vector sum of two or more vectors
SpeedRate of Motion:
Change of position in a given amount of time.
Formula:Speed =
Distance/timeUnits: km/hours, m/s
SpeedAverage Speed
Is computed for the entire duration of a trip
Instantaneous SpeedIs the rate at
which an object is moving at a given moment of time
Speed right now
Speed Practice Problems1. How long does it take a bird to fly 300km if
it travels at a speed of 50 km/hr? 2. Alex rode his bicycle 60 kilometers in 4
hours. How fast was he going?3. Joe can pitch a baseball 32 m/s and the ball
crosses the plate in 1.5 seconds. How far away is the plate?
4. Kayla runs 90 meters with a speed of 15 m/s. How long did it take?
VelocityVelocity= Speed in
a given direction.Velocity is a vectorYou combine
velocities the same way you combine displacementSame direction, add
themOpposite direction,
subtract them
AccelerationRate of change in
velocity. Acceleration is a vector Formula: A = vf – vi or Δv
t tUnit: m/s2
Variables need to solve acceleration problems
2 Velocities Time
DecelerationNegative AccelerationSolve it just like the
acceleration problem but the answer is always
NEGATIVE
Acceleration/ Deceleration Problems1. A car has starts from rest and goes to 20 m/s
in 4 seconds. What is the car’s acceleration?2. A runner starts to run and reaches a velocity
of 100 m/s in 25 seconds? What is the car’s acceleration?
3. A train slows down from 200 m/s to a stop in 50 seconds. What is the car’s deceleration?
4. A train has an acceleration of 40 m/s2 during a period of 15 seconds. What is the train’s velocity?
Centripetal ForcesCentripetal Force is
a force that pulls an object towards the center.
Center Seeking
Constant Speed and Circular Motion
An object moving in a circular motion may have constant Speed even though it is accelerating.
Why?
3 ways objects accelerate Change in Speed only Change in Direction only Change in Speed and Direction
Momentum Momentum is the
product of the mass times the velocity.
The heavier an object, the harder it is to stop its movement.
Formula: Momentum = m x v
ForcesForce is a push or
pull on an object.
Can cause a resting object to move or it can accelerate a moving object by changing the object’s speed or directions
Unit for force:N or Newton.
Balanced forces:Where there are two
forces that counteract each other and result in no movement (EQUAL)
Unbalanced forces: One force is greater
than the other force. (UNEQUAL)
FrictionA force that resist
motion and can cause heat
Lubricant help reduce friction
Types of frictionStaticSlidingRollingFluid
Types of FrictionStatic—is the friction force that acts on objects
that are not movingSliding—is the force that opposes the direction
of motion of an object as it slides over a surfaceRolling—the friction force that acts on rolling
objectsFluid—opposed the motion of an object through a
fluidFluids= water and mixture of gasesFluid friction action on an object moving through
the air is known as air resistance
Newton’s Laws of Motion1st Law: Objects at rest remain at rest, or
objects in motion remain in motion unless acted upon by a force.
2nd Law: The acceleration of a body depends on the ratio of the acting force to the mass of the body.
3rd Law: for every action there is an equal and opposite reaction.
1st Law of Motion (Law of Inertia)Inertia: force that is resistant to the direction of the motion
Unbalanced forces
Examples: Inertia belts (seat belts)
2nd Law of MotionConcept:
Acceleration Unbalanced forces
Examples: hitting a golf ball gently vs. hard.
Answer = ___ newtons
2nd Law of Motion Formula:
Force=mass x acceleration F=ma
1. How much force is needed to accelerate a 500.0 kg car at a rate of 4.000 m/s/s?
2. A 100 N causes an object to accelerate at 2 m/s/s. What is the mass of the object?
3. A 1.5 kg ball is kicked with a force of 450 N. What acceleration did the ball receive?
3rd Law of MotionAction/ Reaction
Concept: Action/Reaction of objects
Balanced forcesExamples:
Stationary objects, rockets being launched
Gravity and Free Falling Objects
Gravity: is a force that acts between two masses
Acts downward towards the center of the Earth
All objects fall at a rate of 9.8 m/s/s
Galileo did an experiment at the leaning tower of Pisa in Italy with bowling balls. Both balls fell at the same rate.
Galileo's experiment at the Tower of Pisa
Air ResistanceForce that slows
down falling objects due to the atmosphere and surface area of the object.
Newton’s Law of Universal GravitationShows that objects
are attracted to one another by their mass and their distance away from the object.
Feather vs. RockEarth: feather
would float down (air resistance) while the rock would drop at 9.8 m/s/s
Moon: feather and rock would drop at same rate due to no atmosphere and air resistance.