Transcript Motion, Acceleration, and Forces - Belle Vernon Area School District

Motion, Acceleration, and Forces
Physical Science
2012-2013
Motion
Section 3-1
• Motion is a change in position of an object
Distance vs. Displacement
Distance
• The total length of the path an object
follows:
Displacement
• The distance and direction of an objects final
position from its initial position
• Displacement includes both a length/size and
direction and is called a vector
What is the actual displacement?
Speed
• The distance an object travels per unit time.
• We use metric (SI) units and it is meters per
second (m/s)
• Usually the speed of an object changes as it
moves from one place to another
Instantaneous Speed
• The speed of an object at a single point in
time
• Speedometer
Average Speed
• The total distance traveled divided by the
total travel time
___
V = d/t
____
V = average speed d=distance
t=time
Practice Problems
• What is the average speed of a car that
travels a distance of 750m in 25s ?
• What is the average speed of a motorcycle
that travels a distance of 300m in 10s ?
• What is the average speed of an airplane
traveling a distance of 1000m in 10s ?
Velocity
• The speed of an object and the direction of
the motion
• Objects have different velocities if they are
moving in different directions or a different
speeds
Graphing Velocity
Time vs. Distance Graph
Acceleration
Section 3-2
• Acceleration is the change in velocity divided
by the time it takes that change to occur
Changing Direction
• A change in velocity can be either a change in
how fast something is moving or a change in
the direction of the movement
Calculating Acceleration
• When an object moves from one place to
another, it might speed up, slow down, and
change directions many times.
• Each change in velocity causes the
acceleration of the object to change
Acceleration Equation
Calculation Positive Acceleration
• An airplane starts at rest and moves down
the runway in a single direction. After
accelerating for 20s it reaches a speed of
80m/s. What is the acceleration?
Calculating Negative Acceleration
• A car is moving in a straight line at a constant
sped of 3m/s and comes to a complete stop
in 2s. What is the acceleration?
Motion and Forces
Section 3-3
What is Force?
• Force is a push or pull that one object exerts
on another
• Force can cause the motion of a object to
change.
Baseball, Tennis, and Billiards
Balanced Forces
• Force does not always change velocity, two or
more equal forces acting on an object in
opposite directions can cancel each other
out. The net force is zero.
Unbalanced Forces
• Unequal forces applied in opposite directions
lead to a net force in the direction of the
larger force and movement in that direction
Friction
• The force that opposes the sliding motion of
two surfaces that are in contact
What Causes Friction?
• Frictional force depends on the materials that
the surfaces are made of and the roughness
of the two surfaces
• All surfaces have bumps and dips in them
that can cause contact and thereby friction
(microwelds)
Frictional Force
• FF increases when the force pushing the
surfaces together increases.
Static Friction
• The frictional force that prevents two
surfaces in contact from sliding past each
other. Once the applied force is greater, the
object will move.
Rolling Friction
• Rolling friction is usually much less that static
friction, that is why we use wheels!
Air Resistance
• This force opposes the motion of objects that
move through the air.
• Air resistance acts in the opposite direction
of the objects movement
• The greater the surface area of the object the
greater the power of air resistance on that
object
More surface area means a slower fall
Terminal Velocity
• As an object falls it accelerates due to gravity,
however air resistance eventually steps in to
slow the object to a speed that no longer
increases…that equaled out speed is called
terminal velocity!