Physics 100 Summary
Theme I: What causes things to move, on Earth and in the Heavens?
What's going on down here and up there?
- Methods of measuring space and time
- Time -- Counting periodic events
- Space
- Distance between two points & Position with respect to an origin.
- Displacement
- Velocity
- Acceleration
- Relationships between Position, Velocity and Acceleration
- Graphical methods: x vs t, v vs t, a vs t
- slope of v vs t graph gives a
- area under v vs t graph gives displacement, change in position
- Algebraic formulae for constant acceleration
- a = dv/dt
- v = a delta-t
- delta-x = vo delta-t + (1/2) a (delta-t)2
- a delta-x = (1/2) (vf2 - vi2)
- Extend these ideas to three dimensions
- Vectors (prototype: displacement) as arrows on a map. Have both length and direction
.
- Vector Properties
- Equal vectors: Same length and direction
- Adding vectors. Tip to tail
- The negative of a vector (reverse direction)
- Subtracting vectors (two equivalent methods)
- Dealing with vector components in an x,y,z coordiante system
- displacement, Velocity and acceleration are vectors,
time, distance and speed are not.
- The "Causes" of motion
- Objects keep moving with constant velocity unless something happens.
Galileo's Law of Inertia or Newton's First Law.
Defines what we mean by "something happening."
- A constant force on something causes acceleration -- constant changes in velocity for equal time intervals
--Newton's first Law of motion
- Verify constant force with a spring between agent and victim
- the amount of acceleration depends on the object --
--this leads to a way of determining "mass": m1/m2 = a2/a1
- Two equal forces in same direction on same object cause double acceleration
- Two equal forces in opposite directions on same object cancel
- If forces are acting on an object in different directions they add like vectors
- F = ma summarizes these observations
- Does this law work in 3-D as well:
Experiment says yes, so F = ma
- Circular motion: centripetal force F = 4 pi2mr/T2
towards centre of circle
- Projectile motion, gravity always down Fg = mg
-- Parabolic trajectory, Horizontal velocity not changing
and vertical velocity is cosntantly accelerating.
- On a spherical earth, a parabolic trajectory becomes an orbit if the
object is thrown faster and faster.
- Newton finds relationship between acceleration of apple on earth and moon
far away from
the earth's center.
- Kepler observes relationship between orbital period and radius: Kepler's Law, R3/T2 = constant
- Galileo observes moons of Jupiter and Newton confirms Kepler's Law
- Result: Universal force law for gravitation true everywhere:
- All objects attract each other.
- For two objects
Fgravity = G mM/R2
- Forces of m on M and of M on m are equal in magnitude and opposite in direction
Theme II: Conservation Laws
- Conservation of energy (Mechanical energy conserved in some situations.)
- Conservation of momentum -- Newtons third laws, Force on a by b = and opposite
to force on b by a.
- These make solving many problems easier
- Suicide Pendulum
- Roller Coaster
- Collisions and explosions
Light
- a simple model with a few rules can explain a lot
Shadows, Pinhole images, Images in a mirror and apparent depth of water
Electrostatics
Another Force law, acts like gravity (1/r2) but different: much larger and can be repulsive or attractive.
Induction and polarization
Hanging Charges
Nailed down charges and superposition of forces.