PHYS 201 STUDY GUIDE FOR PART TWO:
FORCES AND MOTION
INTRODUCTION:
In this second part of the course we consider: (a) two dimensional motion [combining 1-D motion with vectors];
(b) the relation between force and motion [which introduces the concept of mass and Newton's three laws of motion];
and (c) one of the four fundamental forces: gravity.
We begin this section by looking at two dimensional motion. This combines the ideas of position, velocity, and
acceleration with the idea of a vector (having components). We look at three special cases: trajectory motion, uniform
circular motion, and relative velocity.
We next introduce the concept of INERTIAL MASS as a basic quality of matter. It is the quality that determines
how a force will affect the motion of an object. This extremely important relation between force and motion is
contained in a very simple equation: F = m a, called NEWTON'S SECOND LAW. We also consider Newton's first
(which is a special case of Newton's Second Law, and Newton's third law which is important in determining who is
pushing on whom.
As an important example of force, we consider Newton's Law of Gravity and how it relates to the concept of
GRAVITATIONAL MASS.
Next we consider the concept of torque (or angular force) and its relation to rotations and force.
TWO DIMENSIONAL MOTION
OUTLINE:
1) Projectile motion (work in components!) M
a) x(t) and y(t)
2) Uniform circular motion (turning but not speeding up) N
a) frequency
(1) f is frequency in cycles/sec
(2) = 2f, is angular velocity in radians/sec
(3) T = 1/f, T is period in sec/cycle
b) tangential velocity: vtang = r = 2r/T (circular means r=constant so vradial = 0)
c) radial acceleration: aradial = vtang = ²r = vr = vtang²r = v/r ;
d) tangential acceleration causes speed to change, so uniform circular motion means atang = 0
3) Relative velocity (addition of vectors!) O
LETTER PROBLEMS:
M. A ball is thrown from the top of a 14 m high building with a speed of 25 m/s directed at an angle
of 33° above the horizontal. a) How far away will the ball hit the ground? b) How long will it take
the ball before it hits the ground?
N. The earth spins with (approximately) uniform circular motion about its axis. The radius of the
earth = 6,378 kilmeters. a) What is the period of the earth's rotation about its axis? b) What is the
tangential speed of the earth at the equator as it spins? c) What is the angular velocity of the
earth as it spins? d) Is the earth undergoing acceleration as it spins? e) What is the radial
acceleration of the earth at the equator as it spins? f) What is the tangential acceleration of the
earth at the equator as it spins?
O. A boat can travel at a speed of 5 m/sec on a calm lake. a) What direction sould a pilot point
his boat to go directly across a river that flows at a rate of 2 m/sec? b) How long will it take if the
