Chapter 2 Section 1 Describing Motion

When I think of Motion I think of movement and SPEED! Fast Cars or Trucks OR Even Fast People

But exactly how do we determine if something is moving?

By using a Reference Point By using a Reference Point  A stationary object in the background that is not going to move.  We compare the position of the non moving object to that of something that we think is moving.  Examples ?

And now I can define Motion Motion is a change in an object’s position relative to a reference point.

Creating a frame of Reference to measure distance  Frame of reference is a coordinate system in which the position of the object can be measured.  Coordinate System is like a map. The reference point is at the origin (start), and each object’s position can be described with coordinates x and y.

Distance vs Displacement   Displacement is the shortest distance from the initial to the final position. Thus, it is the length of an imaginary straight path, typically distinct from the path actually travelled. Initial Final

Displacement is As the Crow Flies Who is the Crow, Alan or Eva? What is both of their displacements?

What is the displacement of a track star who travels 400m around the track? Blue man is heading home and travels a path of A to B to C. What is his distance traveled? What is his displacement?

SPEED!  Speed is the distance traveled divided by the time it took to travel that distance.  Formula -Speed = distance/time  So in order to measure speed I have to have Distance (km, m) and Time (hr, s)  Units (derived units) mi/hr, km/hr, m/s

Usain Bolt Breaks Olympic Record  If Usain Bolt can run 9.58 seconds in 100 meters what is his speed? DataFormulaWorkAns S=s=d d= t t=

Another Speed Problem  A car traveling at a constant speed (traveling equal distance in an equal amount of time) covers a distance of 750 m in 25 s. What is the car’s speed? DataFormulaWorkAns Work Problems 1-4

Speed can also be calculated by looking at a distance-time graph  Calculate the bikers Instantaneous Speed at B (speed at a given instant-like using a speedometer in a car)

Reading Distance/Time Graphs Speed Graphs

Section 2 Velocity and Momentum

What is Velocity?  A quantity describing both speed and direction. Speed in a given direction.  20 m/s North, or 95 mi/hr towards home plate  Formula is the same as speed plus direction.  Velocity of the object can change even if the speed remains constant, how?

Velocity Problem  What is the velocity of a swimmer who swims exactly 110 m toward the shore in 72 s? DataFormulaWorkAns

Motion of the earth’s crust  Plates move along the San Andreas Fault in California at 1 cm/y  Australian Plates move at 17 cm/y pushing Australia North at a velocity of 17 cm/y North

Relative Motion  A person sitting in a seat on a moving train is a rest relative to the train, but the person is moving relative to the ground.  All depends on your reference point  What are some other situations where you are moving relative to one object and at rest relative to another?

Momentum  Momentum is a commonly used term in sports.  A team that has the momentum is on the move and is going to take some effort to stop.  Momentum is a physics term; it refers to the quantity of motion that an object has. A sports team that is on the move has the momentum. If an object is in motion (on the move) then it has momentum.

Momentum- Physics  Momentum can be defined as "mass in motion."  All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion.  Momentum is dependent upon two variables: Mass and Velocity.  Formula Momentum = mass x velocity  Units Mass(kg) x Velocity (m/s) = kg x m/s  p = m x v Draw Triangle

Momentum Problem A car moving 20 m/s has a mass of 2000 kg, what is the car’s momentum? DataFormula WorkAns Work Momentum problems

Section 3 Acceleration

Acceleration  When you gain speed or slow in a car, your velocity changes.  Velocity also changes when you turn or change directions. (velocity is speed plus direction)  Any change in velocity is acceleration.   Positive acceleration = speed up   Negative acceleration = slowing down

Finding Acceleration  You need velocity at different times  Accel= final velocity - initial velocity time Or a=v t v = final velocity - initial velocity Units for acceleration = m/s Units for acceleration = m/s 2, meters per second squared

Acceleration Math A flower pot falls off a second story windowsill. The flower pot starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the acceleration of the flower pot. DataFormulaWorkAns vf=a = vf - vi vi=t t=

More Math What is the average acceleration of a car that starts from rest and moves straight ahead at 18 m/s in 12 s ? DataFormulaWorkAns vf= a = vf - vi vi= t t=

Graphs Speed graphs are _______ - ________ graphs. Acceleration graphs are _______-______ graphs.

Acceleration Graphs Draw graph and identify acceleration, deceleration, and no acceleration

Motion in 2 Dimensions  Circular motion – a horse on a carousel, its speed remain constant but it is accelerating because its direction is changing.  Centripetal Acceleration – acceleration toward the center of a curved or circular path.

Motion in 2 Dimension  Projectile motion – throwing a ball to someone, curved downward path  The object has horizontal acceleration, then gravity causes it to accelerate downward