WHAT IS MOTION?HOW DO WE DESCRIBE MOTION?

Unit 2 - Kinematics

SP1. Students will analyze the relationships between force, mass, gravity, and the motion of objects. • Calculate avg velocity, instantaneous velocity, and acceleration in a

given frame of reference

• Compare and Contrast scalar and vector quantities.

• Compare graphically and algebraically the relationships among position, velocity, acceleration, and time.

What is Motion?

Motion = a change in positionIn order to describe a change need a Frame

of Reference

EX: Describe the motion of the pencil. vs the Sun vs the Earth

** Most common frame of reference is the surface of the earth

Frame of Reference

Reference point used to compare distances, displacements, speeds, velocities, etc.

To measure motion, one point must be considered as nonmoving

Sports use reference points

Football?Basketball?Baseball?And many others

SCALAR AND VECTOR QUANTITIES

describe magnitude only speed Time distance mass volume

describe magnitude and direction velocity acceleration displacement forces

What is Motion?

Distance – total change in position (how far)

Displacement – total distance from starting point and direction

Distance?

8 m

6 m

2 m

1 m

Displacement?

8 m

6 m

2 m

1 m

Distance vs. Displacement Examples

6 m 3 m

Distance= Displacement = 9 m 9 m right

6 m

3 m

Distance= Displacement = 9 m 3 m left

6 m

3 mDistance= Displacement = 9 m ?

northeast

mc

cmm

cba

71.6

36 222

222

Distance versus Displacement

To determine displacement draw a diagram of the path taken Example: 8 m east, then 6m north, then 2 m east,

then 1 m south

Simplify the diagram to a right triangle

Use Pythagorean Theorem to determine the displacement

8 m

6 m

2 m1 m

Speed and Velocity

speed is the rate at which distance is covered

scalar quantity

velocity is the speed and direction of an object

vector quantity

Descriptors of Speed/Velocity

Instantaneous Velocity velocity at a given point in time

What tools do we use to find the instantaneous speed of a car?Constant Speed

speed that does not changeConstant Velocity

speed and direction do not change – perfect straight line motion

What three controls in our car change velocity?

Acceleration – change in motion

any change in velocity is called acceleration change in speed change in direction

vector quantityhas two units of time in the unit!!!!!!!!!

Acceleration EQ

A car is traveling around a track with it’s cruise control set at 30 m/s. Does the car undergo acceleration?

Sample problem:

In 5 seconds a car moving in a straight line to the north increase its speed from 50 km/hr to 75 km/hr. What is the magnitude of its acceleration?

Free Fall

Falling bodies accelerate due to gravity If a body falls under the influence of gravity

only, it is said to be in Free Fall We ignore air resistance when studying free

fall All bodies in free fall, regardless of weight,

will accelerate at the same rate The acceleration due to gravity is:

g = 9.8 m/s2

Acceleration-Free Fall Equations

When initial velocity is zero, vf = at

TIME (s) VELOCITY (m/s)

0 0

1 9.8

2 19.6

3 29.4

4 39.6