Unit 3 Physics
The coefficient of static friction is always ________________ the coefficient of kinetic friction for any 2 given surfaces.
greater than
What does the amount of friction between two surfaces depend on?
1. Kind of surface 2. Force pressing the two surfaces together
What are the Four major Forms of Friction?
1. Sliding Friction 2. Rolling Friction 3. Fluid Friction 4. Air Resistance
What does a free body diagram show?
All of the forces acting on an object.
In which direction does FN act?
Always perpendicular to the surface the object is resting on.
In which direction does FG act?
Always toward the center of the earth (down).
What is Mass?
Amount of matter in an object
What does Fa stand for?
Applied Force
What are the SI units for Force?
Newtons
What is weight measured in?
Newtons
What is the unit for force?
Newtons (N)
What does Fn stand for?
Normal Force
What is Newton's First Law of Motion?
Objects don't accelerate unless a net force is applied
A Normal Force (FN ) is always _______________ to the surface your object is resting on.
Perpendicular
What is net force equal to?
Product of its mass & acceleration
What is Force?
Push or pull (acceleration)
What is Net Force?
Sum of all forces acting on an object
What is Inertia?
Tendency of an object to resist any change in its velocity
_________ is force along a string, rope, or chain.
Tension
True or False: Mass is the same everywhere, even on the moon?
True
True or False: Objects with more mass have more inertia
True
True or False: The coefficient of friction has no units.
True
True or False: There is no theoretical way to determine coefficients of friction.
True
True or False: Weight is also another form of gravity.
True
Which of the bottom is correct about friction force?
Two surfaces rub against each other and the force acts OPPOSITE the direction of motion (similar to air resistance).
When does acceleration occur?
Unbalanced forces
What are some examples of surfaces that have a coefficient of friction of zero or considerable close to zero? Choose the best 2.
air hockey table & ice
Newton's First Law states that an object in motion will...
stay in motion.
What does Ff stand for?
Frictional Force
What formula is used when trying to find Acceleration?
a=F/m
What is N/N?
1
What does Fg stand for?
Force of gravity (Mass x ag)
What is weight?
Force upon an object due to gravity
Calculate the force of friction for a surface with a coefficient of 0.4 when FN= 25 N. Ff = ?
10 N
Which of these values for coefficient of friction is probably NOT correct?
3.1
What is the highest published coefficient of friction?
4
What is applied force?
A push or a pull by a person or animal
Newton's 2nd Law is also called the Law of ______________ and is centered around the equation F = ma.
Acceleration
What is Newton's Second Law of Motion?
Acceleration of an object is directly proportional to the NET FORCE & Inversely proportional to the MASS of the object.
Newton's 3rd Law is also called the Law of ______________ and deals with equal and opposite forces.
Action-Reaction
What is Acceleration?
Change in velocity
Are Mass and Inertia inversely or directly proportional?
Directly Proportional
What formula is used when trying to find Force?
F=ma
What other force is acting on the box in the Y direction?
FN
True or False - an object that has arrows of equal length but in opposite directions has a net force greater than zero.
False
True or False: More mass = less inertia
False, more mass = more inertia
Looking at this body diagram, how do we know the box is accelerating to the left?
Fapp arrow is greater than Ff.
What is the Third Law of Motion?
For every action FORCE, there's an equal & opposite reaction FORCE (comes in pairs)
Newton's 1st Law is also called the Law of ______________ and deals with an objects tendency to continue doing what it's doing.
Inertia
If all the arrows are the same length, what is the motion of the box.
It is not moving OR moving at a constant velocity. (Balanced Forces)
What is the unit for mass?
Kilograms (kg)
The Force of friction equals
The coefficient of friction times the Normal Force
What is Friction?
The force that acts between two surfaces as they move past each other
Why is it more difficult to get something moving than to keep it moving?
The max value of the coefficient of static friction is always greater than the coefficient of kinetic friction. So the force required to get something moving is greater than the force required to keep it moving.
Which is greater, the force of her finger on the table, or the force of the table back on her finger?
The two forces are equal.
What is the ideal method of determining the coefficient of friction for two materials?
Trials, time to experiment!
What did Galileo state?
When friction is present, a force is needed to keep an object moving.
What is SLIDING friction?
When you exert enough force to overcome the microwelds and the object starts to move. (opposes the motion of two surfaces)
Why is friction a good thing?
You need friction in order to have motion
A coefficient of friction of zero would mean ___________.
a frictionless interaction.
Why does Friction occur?
b/c of the attraction between two surfaces
Is it easier (requires less force) to start an object moving or to keep an object moving?
keep an object moving
The ___________ of the arrow is the magnitude of the force in a certain direction.
length
What is the unit for acceleration?
m/s² or kg/h²
What formula is used when trying to find Mass?
m=F/a
Friction depends on
type of materials interacting
What is the symbol for coefficient of friction?
μ