Mechanics

MECHANICS the sub branch of classical physics that is concerned with the forces acting on bodies , whether at rest or in motion. is divided into statics, kinematics and dynamics

1.STATICS- focuses on the way in which forces combine with each other so as to produce equilibrium.

1.KINEMATICS- focuses on the motion of a body without regard to the cause of that motion

DYNAMICS- focuses

on the way in which forces

produces motion.

MOTION defined as the movement of an object exhibited by a change in position

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

MOTION IS RELATIVE it may be described by specifying how far something has traveled in changing position and time. 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.

DISTANCE AND DISPLACEMENT

1.DISTANCE - the total path length traversed by an object moving from one location to another

- a scalar quantity which has only magnitude.

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

FINISHNeed to distinguish how long we traveled from how far away (and in what direction) we traveled.

your home

your school

A displacement has

Size = length of this arrow

displacement from home to school

2 Displacement and distanceTo go to school from home...

size & direction.

Distance = length of path you travelled( size of displacement)

l1l2l3

2 Displacement and distanceTo go to school from home... your

home

your school = l1 + l2 + l3

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.

SAMPLE PROBLEM:1.On his way to school, Jed traveled 100 m North, 300 m East, 100 m North, 100 m East , 100 m North.

a. Find the total distance traveled by Jed.

b. Determine the displacement made by Jed.

SPEED AND VELOCITY:• SPEED- a scalar quantity which

measures how fast something is moving.

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

•VELOCITY- a vector quantity that represents a rate of change of displacement.

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.

How far has the

car traveled

in 15 seconds?

4.A car traveled at 88 km/hr for 5 hours. How far did it travel?

4.Justin walks 5 km/hr. How long did it take him to travel 15 km?

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)