ACADECScience w/ Ms. Hendryx

9/8/11

UNITS (DIMENSIONAL ANALYSIS)

1. What am I asked for? What units?2. What do I know? What units do I

have to work with?3. What do I need to know? What units

are missing?4. Solve!

UNITS (DIMENSIONAL ANALYSIS)

There are 8 slurps in a burp, and there are 5 burps in a farkle. 3 farkles are equal to 4 bonks. If I have 2 bonks, how many slurps do I have?

UNITS (DIMENSIONAL ANALYSIS)

Force has units of Newtons. A Newton is defined as (kg*m)/s2. If I have a ball with a force of 3 Newtons moving with a velocity of 10 m/s for 2 seconds, what is the mass of the ball?

UNITS (DIMENSIONAL ANALYSIS)

Position and Displacement

Velocity Acceleration

Definition

Distance with direction

Speed with direction

Change in velocity with respect to time

Units m (units of distance)

m/s(units of speed)

m/s2

(units of velocity divided by units of time)

REVIEW KINEMATICS:

v = v0 + at

Δx = ½(v0 + v)t

Δx = v0t + ½at2

v2 = v02 +2aΔx

What is an object’s acceleration if it begins at rest and reaches 10m/s in 5s?

UNITS (DIMENSIONAL ANALYSIS)

What is an object’s final velocity if it begins at 3m/s and accelerates at 2m/s2 for 4s?

What was the original velocity of an object that traveled 2m at an acceleration of 5m/s2 and reached a final velocity of 6m/s?

UNITS (DIMENSIONAL ANALYSIS)

KINEMATICS

Which equation solves for the time it takes for a ball to reachthe ground if thrown horizontally at 5m/s from a height of25m?

a. -25m = -5m/s(t) + . (9.8m/s2)t2

b. 25m = 5m/s(t) + . (9.8m/s2)t2

c. 25m = 0 + . (9.8m/s2)t2d. -25m = 5m/s(t) + . (-9.8m/s2)t2e. 25m = 5m/s(t)

PRACTICEWhen solving two-dimensional motion problems, the variable that remains the same in both the x- and y-directions is

a. velocityb. displacementc. accelerationd. timee. momentum

NEWTON’S LAWS

1. Objects in motion stay in motion, and objects at rest stay at rest unless a force is applied. (Constant velocity unless a force is present)

2. F = ma

3. For every action, there is an equal and opposite reaction.

IMPORTANT FORCES:

GRAVITY: F = mgg = -9.81 m/s2

FRICTION (only works as opposing force):

Static—before the object starts moving (block on a ramp)

Kinetic—after the object starts moving (block on a ramp; air resistance)

NORMAL FORCE:Supporting force (perpendicular

to surface; book on desk)

PRACTICEYou strike a golf ball with 150 N of force, at an angle of 30 degrees above the horizontal. As a result, the golf ball exerts

a. a force of 150 N at an angle of 30 degrees above the horizontal on your golf club

b. a force of 150 N at an angle of 0 degrees above the horizontal on your golf club

c. a force of 150 N at an angle of 30 degrees below the horizontal on your golf club

d. no force on your golf club; otherwise the ball would not move

e. no force on your golf club; otherwise your golf club would fly backwards

PRACTICEIgnore air resistance effects. A ball is thrown straight up into the air at 5 m/s. At the highest point in its trajectory,

a. velocity is zerob. velocity is constantc. acceleration decreasesd. acceleration is zeroe. acceleration increases

FORCE DIAGRAMDraw arrows corresponding to the forces acting on the blocks:

m

m