Download II. Acceleration

FORCE
Definition:

A push or a pull
Force can cause motion

SI unit -> Newton (N)= 1 kg x 1 m/s2

Sometimes pound (lb) can be used as a unit for force

1 Newton=0.22481 pounds force

COMBINING FORCES
B.
Balanced Force


Equal and opposite forces = ‘balanced’
Balanced forces give no motion
No motion of hands
COMBINING FORCES

Unbalanced force – more force in one direction (net
force)
NET FORCE
Bigger force to the right
 Smaller force to the left
 Net force to the right

III. FRICTION AND GRAVITY
A.
Friction – a force that opposes motion
1.
2.
Caused by the interaction
between two touching surfaces
rubbing against each other
Four Types
A.
STATIC
Friction
that acts on something
that is not moving
No heat or wear is generated
B.

SLIDING
Force resulting when pushing or pulling an object
over a surface.
C.

ROLLING
Contact is reduced because of rollers or wheels or ball
bearings.
D.
FLUID FRICTION
Resistance from a “fluid”
 Fluids are liquids and gases.

REDUCING FRICTION
A smooth surface does not demonstrate as much
friction as a rough surface.
 Waxing, oiling, etc. can be used to reduce friction.

COEFFICIENT OF FRICTION


1.
2.

µ= “coefficient of friction”  represents the
roughness of the surfaces in contact.
In reality there two main subtypes:
µs - Static friction to get it moving
µk- Kinetic friction to keep it moving
µs > µk needed for movement to occur
B.
Gravity
– force of attraction between two objects
---> pulling force
Factors Affecting Gravity
a. Mass – more mass, more gravity
b. Distance – closer, more gravity
http://www.exploratorium.edu/ronh/weight/
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1. Describe three ways in which a car’s velocity
will change
2. Identify a one situation involving unbalanced
force and one situation involving balanced force.
Explain how it each affect the motion of an
object.
3. Arrange the following pairs of surfaces in
order of most friction to least friction
A shoe sole and a waxed basketball court
 A shoe sole and the frozen surface of a lake
 A shoe sole and the sidewalk
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END CHECK- COMPLETE ON SEPARATE
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4. Explain why Venus, which is slightly less
massive than Earth, experiences a stronger
gravitational pull from the sun than Earth does.
5. What is the average acceleration of a scooter
that starts at rest and moves straight ahead at
12 m/s in 24 s.
6. Which will be moving faster after 3.0 s, a
cyclist maintaining a constant velocity of 15 m/s
straight ahead or a race car accelerating forward
from a stoplight at 4.0 m/s2?