Studied by 8 people
origin of normal contact forces
electrical, interactions between electrons/particles/atoms
drag force
the force acting against the motion of n object that is moving through a fluid (gas or liquid), e.g. air resistace
what factors affect the magnitude of drag forces
speed and shape of the body
how are speed and drag forces proportional
directly
Stokes Law
An equation relating to the terminal settling velocity of a smooth, rigid sphere in a viscous fluid of known density and viscosity to the diameter of the sphere when subjected to a known force field
viscosity
a liquid's resistance to flow
how does temperature affect viscosity?
Viscosity increases as temperature decreases and vice versa
Buoyant force
the force acting on an object in a fluid due to a difference in pressure at the top and bottom of the body; the force is opposite to weight
when will a body float?
buoyant force is equal to the weight of the body
Newton's first law of motion
when the net force on a body is zero, the body will move with constant velocity (which may be zero), it will move on a straight line with constant speed
inertia
the tendency of a massive body to remain in its current state of motion, a mass tens to stay in the state on motion it was in before a force acted on it
Newton's third law of motion
if body X exerts a force on body Y, then body Y will exert an equal and opposite force on body X
equal and opposite forces in 3rd law
must be acting on two different bodies (not on the same object, different from net force)
Newton's second law of motion
the net force on a body of constant mass is proportional to that body's acceleration and is in the same direction as the acceleration
unbalanced force
Forces that produce a nonzero net force, which changes an object's motion
translational equilibrium
net force acting on a body is zero (non-zero velocity but constant, zero acceleration)
force
the action of one body to a second body, unbalances forces cause change in velocity or shape, a vector quantity
weight
the gravitational force between a body and the planet the body is on, direction downwards
the difference between mass och weight
mass is the same everywhere but weight depends of the gravitational force (the size of the planet)
tension
the force arising when a body is being stretched or compressed (two forces acting on it, opposite directions)
how do springs return to their original shape and lenght?
when they're compressed or streched >> tension is formed >>brings the spring back to its initial lenght
Hooke's law
the tension in a spring is proportional to the extension or compression
normal contact force
the force that arises when two bodies are in contact directed normally to the surface creating the force
free-body force diagram
a diagram showing all the forces acting on an object (magnitudes and directions)
equilibrium
a state in which opposing forces or influences are balanced, resultant or net force is zero, velocity is zero
resultant or net force
the one force whose effect is the same as that of a number of forces combined
friction forces
the force that opposes motion between two surfaces that are touching each other
two types of friction
dynamic and static friction
dynamic friction
a force opposing motion when a body moves
when is friction present?
When an object is in motion (in contact with another surface) or when someone is attempting to move an object (tendency for motion)
static friction
a force opposing the tendency for motion when a body is at rest
Friction laws
Empirical 'laws' about frictional forces.
what are the four friction laws?
1. area of contact does not affect friction
2. equation for dynamic friction (normal force and coefficient of dynamic friction)
3. speed does not affect the force of dynamic friction
4. equation for static friction
coefficient of dynamic friction
the ratio of the force of friction to the normal contact force on a body that is sliding along a surface
coefficient of static friction
the ratio of the maximum force of friction between two bodies to the normal contact force when an object is at rest
what does the equation of static friction actually give?
the maximum possible static friction that can develop between surfaces, hence an inequality sign in the equation
how are the magnitudes of dynamic and static friction related?
dynamic friction is always smaller than static friction
how to see the amount of static friction from a friction vs. force applied -graph
the maximum amount of friction
how to see the amount of dynamic friction from a friction vs. force applied -graph
constant value (horizontal line)
motion when static friction is present
no motion, the object is at rest
motion when dynamic friction is present
accelerated motion
factors that affect friction
mass and the material of the surfaces in contact with each other
forces acting on a block on a slope
normal force (R), weight (W) and friction (Ff)
components of weight vector
cos and sin
Note
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