Motion Chapter 8.1 Speed Velocity Momentum

Speed  Distance traveled divided by the time during which motion occurred

Speed  Constant speed  object travels the same distance in the same amount of time  Objects at rest have a speed of 0 m/s

Speed Equation Distance Time Speed = v = d t

Speed Example  Suppose a wheelchair racer finishes a 132 m race in 18 s. What was the racer’s average speed?

Speed Example  speed = d/t  Speed = 132 meters/18 s  Speed = 7.3 m/s

Are speed and velocity the same?  A car travels at a constant speed of 30 miles/hour. The car makes a left at a speed of 30 miles /hour.

Are speed and velocity the same?  Speed did not change  Velocity did change

Velocity  Quantity describing both speed and direction  Same calculation as speed & direction.

Velocity Example  Find the velocity of a swimmer who swims exactly 110 m toward the shore in 72 s.

Velocity Example  V = d/t  V = 110 meters/72 seconds  Speed = 1.5 m/s  Velocity = 1.5 m/s towards the shore

Momentum  product of an object’s mass and its velocity  The greater the mass or the faster the velocity, the greater the momentum

Momentum Equation Momentum = mass x velocity Equation is p=mv p is used to represent momentum

Momentum Example  Find the momentum of a 75 kg speed skater moving forward at 16 m/s.

Momentum Example  momentum = mv  Momentum = (75 kg)(16m/s)  Momentum= 1200 kg m/s forward

Conservation of Momentum  The total amount of momentum in a system is conserved

Conservation of Momentum  If two vehicles with different masses are traveling with different velocities and they hit head on, the momentum of the two cars before the collision is the same after the collision.

Acceleration and Force - Chapter 8.2 Acceleration Force Friction and Air-resistance Gravity

Acceleration  change in velocity divided by the time in which the change occurred  The greater the acceleration the faster the object is speeding up.

Acceleration If the speed remains constant, acceleration is zero. SI unit is meter/second per second (m/s/s or m/s 2 )

Acceleration Equation ∆ velocity Time Acceleration = a = V f -v i ΔtΔt

Acceleration Example  Find the acceleration of a northbound subway train that slows down from 12 m/s to 9.6 m/s in 0.8 s.

Acceleration Example  a = change in v/t  Acceleration = (9.6 – 12m/s)/0.8s  Acceleration = -3 m/s 2 or m/s/s

For constant velocity Zero Acceleration

Accelerating has positive slope

decelerating has a negative slope

Force  The cause of acceleration or the change in an object’s velocity  SI unit of force is a newton. (N)

Force  Two Types: 1. Balanced forces do not change motion

Force 2. Unbalanced forces result in a net movement in one direction.  This occurs because the net force on one side is less than the net force on the other.(ex. Tug of War.)

Friction  the force between two objects in contact that opposes the motion of either object  friction maintains balanced forces

Gravity  Gravitational force is determined by the distance between the two masses.  Everything falls at an acceleration of 9.8 m/s 2 in the absence of air resistance  Gravity is opposed by air resistance

Gravity Experiments The Physics of Falling =yXnbvZx9iWs

Horizontal motion has no affect on gravity

Gravity has no affect on horizontal motion.

Gravity only works if you look down. True or False

FALSE

Air Resistance Air resistance is a form of friction Air resistance opposes gravity. Objects with bigger volumes or smaller densities can experience more air resistance.

Laws of Motion - Chapter 8.3 Newton’s 1 st Law Newton’s 2 nd Law Newton’s 3 rd Law

Newton’s 1 st Law unbalanced An object at rest remains at rest and an object in motion maintains its velocity unless it experiences an unbalanced force. Inertia

Newton’s 2 nd Law  The unbalanced force acting on an object equals the object’s mass times its acceleration.  F=ma

Measuring Force  Force is measured in newtons.  1 N=1 kg*m/s 2

Force Example  What is the force necessary for a kg automobile to accelerate forward at 2.0 m/s 2 ?

Force Example  Force= ma  Force = (16000 kg)(2.0m/s 2 )  Force = N

Free Fall the motion of a body when only the force of gravity is acting on it. Acceleration of gravity is 9.8m/s 2 Everything will fall at this acceleration

Mass vs. Weight  Mass represents the measured amount of matter in an object.  Weight is the gravitational force an objects experiences based on its mass.

Mass vs. Weight  Weight = mass x gravity  w=mg, weight is a force.

Terminal Velocity  The maximum velocity reached by a falling object.

Terminal Velocity  This occurs when air resistance is equal to the force due to gravity.  Terminal Velocity of a skydiver is ~200 miles/hr

Newton’s third Law  For every action there is an equal and opposite reaction  Rockets move as a result of action and reaction.

Inertia and a roller coaster