MECHANICS <ul><li>the sub branch of classical physics that is concerned with the forces acting on bodies , whether at rest or in motion. </li></ul><ul><li>is divided into statics, kinematics and dynamics </li></ul>
<ul><li>STATICS - focuses on the way in which forces combine with each other so as to produce equilibrium . </li></ul>
<ul><li>KINEMATICS - focuses on the motion of a body without regard to the cause of that motion </li></ul>
DYNAMICS - focuses on the way in which forces produces motion.
<ul><li>MOTION </li></ul><ul><li>defined as the movement of an object </li></ul><ul><li>exhibited by a change in position </li></ul>
Motion or Movement is a Change In Position 10 ft. Position A Position B
There are many ways of describing motion: 1. Rectilinear motion- the motion of an object traveling at a straight path. 2. Curvilinear motion- an object traveling in a curved path 3. Angular motion - an object traveling at certain angles
<ul><li>MOTION IS RELATIVE </li></ul><ul><li>it may be described by specifying how far something has traveled in changing position and time. </li></ul><ul><li>a reference frame is a physical entity such as the earth’s surface, the deck of a ship or a moving vehicle to which the position and the motion of an object is relative. </li></ul>
<ul><li>DISTANCE AND DISPLACEMENT </li></ul><ul><li>DISTANCE - the total path length traversed by an object moving from one location to another </li></ul><ul><li>- a scalar quantity which has only magnitude. </li></ul>
2. DISPLACEMENT- refers to the straight line distance between the starting and end points. - a vector quantity which has both magnitude and direction
Distance and Displacement START FINISH Need to distinguish how long we traveled from how far away (and in what direction) we traveled.
2 Displacement and distance your home your school A displacement has Size = length of this arrow displacement from home to school To go to school from home... size & direction .
2 Displacement and distance Distance = length of path you travelled ( size of displacement ) l 1 l 2 l 3 To go to school from home... your home your school = l 1 + l 2 + l 3
Suppose we have two towns A and B 10 km apart on either side of a hill. They are joined by a railway line that is straight, and goes through the hill in a tunnel. The road goes round the hill and the total journey distance is 25 km.
So the distance is 25 km. The displacement (the straight-line distance in a particular direction) between A and B is 10 km due East.
If we go from A to B and back again, the distance is 50 km, but the displacement is 0.
<ul><li>SAMPLE PROBLEM: </li></ul><ul><li>On his way to school, Jed traveled 100 m North, 300 m East, 100 m North, 100 m East , 100 m North. </li></ul><ul><li>a. Find the total distance traveled by Jed. </li></ul><ul><li>b. Determine the displacement made by Jed. </li></ul>
<ul><li>SPEED AND VELOCITY: </li></ul><ul><li>SPEED- a scalar quantity which measures how fast something is moving. </li></ul>
SPEED-the rate at which distance is covered at a given time
average speed- defined as the total distance traveled divided by the time it took to travel the distance.
the speed of a body at any instant. Instantaneous speed
<ul><li>VELOCITY- a vector quantity that represents a rate of change of displacement. </li></ul>
Problems: 1. Rachel watches a thunderstorm from her window. She sees the flash of lightning bolt and begins counting the seconds until she hears the clap of thunder 5.0 seconds later .
Assume that the speed of sound in air is 340 m/s and light was seen instantaneously. How far away was the lightning bolt?
2. A car starts from rest and attains a speed of 50m/s in 15 seconds.
<ul><li>A car traveled at 88 km/hr for 5 hours. How far did it travel? </li></ul>
<ul><li>Justin walks 5 km/hr. How long did it take him to travel 15 km? </li></ul>
6. A car travels a distance of 40 km from Manila to a town in Laguna. What is its average speed (in km/hr) if traveling time is from 7:00 A.M. to 7:30 A.M.? its average velocity (km/hr).
Suppose that after a business talk with a friend , the driver of the car drives straight back to Manila from 11:55 A.M. to 12:20P.M.What was the car,s average speed (km/hr) during the roundtrip? its average velocity (km/hr)