Forces and Newton's laws

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