Honors Physics: Chapter 4
describes the relationship between the motion of objects in our everyday world and the forces acting on them
a push or pull
force is a __________ quantity.
gravity, charges, magnets
1. Strong nuclear force
2. Electromagnetic force
3. Weak nuclear force
What are the four fundamental forces of nature (field)?
strong nuclear force
strongest force; attractive force that holds the nuclei of atoms together.
long-ranged but weak; attractive or repulsive force between objects carrying electrical charge.
weak nuclear force
very short range and very weak; responsible for radioactive decay.
always attractive, and acts between all matter in the Universe; weak, but very long ranged; it's the dominant force in the universe for shaping galaxies and stars.
the tendency of an object to continue in its original motion (or resist change in motion)
__________ is a measure of inertia
inertia is a ___________ quantity
SI units for inertia are _____
Newton's First Law of Motion: Law of Inertia
an object at rest stays at rest and object in motion stays in motion unless acted upon by a net external force.
the sum of all forces on an object
1st law implications
1. Space objects will move forever once set in motion.
2. Friction and air resistance are the net forces that usually slow objects.
Newton's Second Law of Motion
If a constant force is applied to an object,
it will ACCELERATE
If ΣF (net force) = 0, then there is
force units are measured in ____________
the gravitational pull on an object; always points straight down
mass is ____________; weight depends upon the ___________.
Newton's Third Law of Motion
1. Every action has an equal and opposite reaction
2. Forces always occur in pairs
3. Action and reaction forces must occur on 2 separate objects
4. Equal in magnitude but opposite in direction
free body diagram
a drawing showing all forces on an object
force of surface on object
1.Perpendicular to surface
2. Acts opposite to gravity
force on a rope
the tension on a rope is the __________ at all points on the rope.
conculsions of the force table demo
1.Balancing forces involves vector addition.
2.The sum of the forces involves considering x- and y-direction forces.
3.Objects in equilibrium have their forces balanced in both x- and y- directions.
Means ΣF = 0
there is no acceleration.
(there must be no net torque too)
not moving; a=0
constant velocity; a=0
Assumptions with Newton's Laws
Objects behave as particles
Masses of strings are negligible
Interested only in the forces acting on the object
(neglect reaction forces)
resistance to motion
surface imperfections and intermolecular forces
friction is caused by......
2. normal force of each surface on the other
factors of friction
force of friction (f)
The direction of the f is opposite the direction of motion
Friction is proportional to the normal n
f = µ n (fyi 0 < μ < 1)
static friction (fs) is ___________ than kinetic friction(fk)
µ depends on the _________ of surfaces in contact
The µs and µk are _____________ of the area of contact
acts to keep the object from moving; if Fa increases, so does ƒs
acts when the object is in motion; f is constant while in motion
*Set the x-axis along the incline and y-axis perpendicular to the incline
*Normal points along y-axis
*Weight points straight down (break into components)
*Friction acts along x-axis
objects accelerating _________ seem heavier.
objects accelerating ___________ seem lighter.
________ scales display the normal force; they are they are the same when a=0.
Weight down and Drag/Air Resistance up
falling objects have 2 forces on them: What are they?
objects don't accelerate downward forever - at some point their velocity becomes _____________.
When the upward Fair resistance = the downward Fgravity, the Fnet = ____.
an object's terminal velocity depends on the object's _____________.
a human's terminal velocity is about 150 mph; an ant's is so low that it can fall far and not get hurt.
non-moving fluids (ex. pressure, floating)
a gas or liquid (both flow)
a force pushing against a specific area of a surface. (force/area)
caused by 100 km of air above us
pressure and depth
the force exerted by a fluid depends on the height of fluid above it; the deeper the object, the more pressure.
acts upward on an object in a fluid making an object feel lighter.
The buoyant force on an object equals the weight of water displaced by the object.
your weight in water
(it's less than your weight in air because FB pushes upward)
buoyant force and the weight
Whether an object sinks or floats depends on the .........
If the object is less dense than the fluid,
the object experiences a net _____________ force
If the object is more dense than the fluid:
The net force is ______________, so
The object accelerates _________________
If an object's weight > buoyant force, then it ________.
If an object's weight < buoyant force, then it _______.
*The object is in static equilibrium
*The upward buoyant force is balanced by the downward force of gravity
moves fluid by changing the pressure in the fluid
When you apply a force to a confined fluid (a closed system), that pressure is applied equally to all parts of the fluid
Pressure is transferred through a fluid.
An applied small Force on a small Area transmits a big Force on a big Area.
Ex: car brakes, car lift
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