Physical Science

Introduction to the wonderful world of Physics

Motion

Objectives:

Explain the relationship between motion and a frame of reference

Relate speed to distance and time

Distinguish between speed and velocity

Solve problems related to time, distance, displacement, speed, and velocity

Motion

• An object’s change in position relative to a reference point

• Observing Motion

• Reference point- a stationary object

aa.k.a reference frame

Direction

• Direction- a description of the direction of an object in motion with a reference directions

• Typical reference directions:

• North, South, East, West, up, or down

Distance vs. Displacement

• Distance-measures the path taken

• Displacement- the change in position of an object

• Displacement must be a straight line

• Generally, displacement is shorter than the distance traveled

Displacement

• Displacement must be in a particular direction, direction must always be indicated

• Ex) toward, away from, east of, west of, north of, south of, etc…

Speed

• Speed- the distance traveled divided by the time interval during which motion occurred

• Speed describes how fast an object moves

• SI unit : meters per second (m/s)• Kilometer per hour (km/h) or • Miles per hour (mi/h)

Constant Speed

• Constant speed- means that the speed does not change

Graphing

• Dependent variable (y-axis) distance– Vertical

• Independent variable (x-axis) time– HorizontalThe speed of an object can be found by

calculating the slope of the line

The slope of any distance vs. time graph gives the speed of an object

Speed and Velocity

• Equation for average speed :– Speed = distance/ time

• Velocity = distance/ time

• Velocity- the speed of an object in a particular direction

Velocity

• Velocity gives the speed and direction of motion

• Ex) Chuck ran 3.5m/s north of the flood

• Direction can be measured as an angle from a fixed line. It can be described as positive or negative along a line of motion.

Velocity

• Velocity is considered to be positive in the direction of motion

• It is negative if moving in the opposite direction of motion

Calculating Velocity

• V=d/t t=d/v d=vt

• * if asked for displacement, you must specify direction

• Write these equations on your index card!

Practice Problem

• Metal stakes are sometimes placed in glaciers to help measure a glaciers’ movement. For several days in 1936, Alaska’s Black Rapids glacier surged as swiftly as 89 meters per day down the valley. Find the glacier’s velocity in m/s. *Remember to include direction!

• Given: time t=1 day• Displacement d= 89 m down the valley• Unknown: velocity v=? (m/s and direction)

Practice problem

• t= 1 day convert to seconds

• Show in scientific notation x 10 s

• Speed=displacement /time =d/t

• V=d/t 89m/ s

• V= m/s down the valley

Practice problems

• Complete # 1-3

• On page 323

Resultant Velocities

• A. When you have two velocities that are in the same direction, add them together to find the resultant velocity, which is in the direction of the two velocities

» → 15m/s » → 3.5 m/s» = 18.5m/s east

»

• B. When you have two velocities that are in opposite directions, add the positive velocity to the negative velocity to find the resultant velocity, which is in the direction of the larger velocity

» ← -2.5 m/s» → 16 m/s

» = 13.5 m/s east