Jan 18, 2018
MotionMotion• MotionMotion
– Occurs when an object changes position relative to a reference point
– Don’t have to see it move to motion took place
Motion• Distance
– Describes motion– How far did the object
move?– SI unit is the meter (m)
Distance vs Displacement
• Displacement– Distance and direction
of an object’s change in position from the starting point
Speed• Speed
– Distance an object travels per unit of time
– Speed = distance ÷ time– s = d/t– Unit of measurement is
meters/second (m/s)
Speed Formula
=
Speed Word ProblemsSPEED = d/t TIME = d/s DISTANCE = s x t
1. If a car travels 400m in 20 seconds, how fast is it going?
2. How long did it take you to walk 100 meters if your speed is 2 m/s?
3. What is the distance traveled if you walk 1.5 m/s in 45 seconds?
Average Speed
• Average Speed– Describes speed that’s
changing– Total distance ÷ total
time– S = d/t
Instantaneous Speed
• Instantaneous Speed– Speed at a given point
in time
– Measured by speedometers
Velocity
• Velocity– Speed and the direction of an
object
– Velocity = distance ÷ time
– How are speed and velocity different?
• Speed and Velocity
Distance/Time Graph
Acceleration
• Acceleration– Rate of change of
velocity (speed and direction)
– Speeding up, slowing down and changing directions
– Can be positive (+) or negative ( - )
– SI unit = m/s 2
Acceleration Formula
• A = acceleration• Vf = final velocity
• Vi = initial velocity• T = time
Acceleration Problems1. A cars velocity changes from o m/s to 30 m/s in 10 seconds.
Calculate acceleration.
2. If a speeding train hits the brakes and it takes the train 39 seconds to go from 54.8 m/s to 12 m/s what is the acceleration?
3. (Be careful!) How long will it take a car to go from 0 to 44 km/hr if they are accelerating at 5 km/hr2?
4. In 1970, Don “Big Daddy” Garlits set what was then the world record for drag racing. He started at rest and accelerated at 16.5 m/s² (about 1.68 times free-fall acceleration) for 6.5 s. What was Garlits’s final speed?
Motion and Force• Force
– Push or a pull
OR
Does every force produce motion??
Force• Net Force
– Sum of two or more forces acting on an object
• Balanced Force– No motion
• Unbalanced Force– Motion
Inertia
• Inertia– The tendency of an
object to resist any change in its motion
– In motion, wants to stay at same speed and in same direction
– At rest, wants to stay at rest
Newton’s First Law of Motion
• Newton’s 1st Law– Object moving at a constant
velocity keeps moving at that velocity unless an unbalanced force acts upon it
– Law of Inertia
– What are the unbalanced forces acting on the baseball that changes its motion?
Newton’s First Law
• In other words . . .– An object in motion
stays in motion, an object at rest stays at rest, unless acted on by an unbalanced force
• Why do we wear seatbelts?
Newton’s Second Law of Motion
• Newton’s 2nd Law– The acceleration of an
object is in the same direction as the net force and is inversely proportional to its mass
– Shows relationship between force, mass and acceleration
Newton’s Second Law of Motion
• In other words . . .– An object will accelerate
in the same direction as the force
– The more massive an object, the slower it accelerates
– The less massive, the faster it accelerates
Newton’s Second Law of Motion
Newton’s Second Law of Motion
Force = Mass x Acceleration
Standard Units of Force• Force
– Measured in Newtons (N)– 1 Newton = 1 Kg m/s2
- Mass in Kg- Acceleration in m/s2
What exactly is a Newton?
0.2248 pounds = 1 Newton of force1 kN = 224.8 lbs of force4 Physical Science books=100 NewtonsJumbo jet = 3.4 million Newtons
150 pound person= about 668 Newtons
Newton’s Second Law Word Problems
1. If the mass of a helicopter is 4,500 kg and the net force on it is 18,000 N, what is the helicopter’s acceleration?
2. What is the net force on a dragster with a mass of 900 kg if its acceleration is 32 m/s2?
3. A car is being pulled by a tow truck. What is the car’s mass if the net force on the car is 3,000 N and it has an acceleration of 2.0 m/s2?
Forces
• 3 forces that oppose motion– Friction– Air Resistance– Gravity
Friction• Friction
– force that opposes motion of two surfaces that are touching
– Friction
• 3 types of friction– Static – Sliding– Rolling
Static Friction
• Static Friction– Force that prevents two
surfaces from sliding– No motion– Caused by microwelds
between two surfaces
Sliding Friction
• Sliding Friction– Force that opposes the
motion of two surfaces sliding past each other
– Microwelds break and reform
– Slows down motion
Rolling Friction
• Rolling Friction– Force between a rolling
object and the surface– Slows down motion
Friction
What would happen if wehad no frictional forcebetween objects?
Air Resistance
• Air Resistance– Opposes motion of
objects that move through the air
– Depends on speed, size, and shape of object
Terminal Velocity
• Terminal Velocity– Falling at a constant
speed– Highest speed a falling
object will reach– Depends on size, shape
and mass of object
Gravity
• Gravity– Attractive force between
two objects– Depends on
• Masses of objects• Distance between them
– Isaac Newton formulated Law of Universal Gravitation
Gravity• Gravitational Acceleration
– Without air resistance, everything falls to Earth at 9.8 m/s2
– So, acceleration due to gravity (g) = 9.8 m/s2
– Force of gravity (N) = mass (kg) x acceleration of gravity (m/s2)– F = m x g
Weight
• Weight– Gravitational force
exerted on an object– Weigh less on the moon– Weight (N) = mass (kg) x
acceleration of gravity (m/s2)
– W = m x g
Mass Vs. Weight
• What is the difference in mass and weight?
mass – amount of matter an object contains
weight- force of gravity on an object
Centripetal Force
• Centripetal Acceleration– Acceleration toward the
center of a curved path
• Centripetal Force– Net force exerted
toward the center of a curved path
Newton’s Third Law of Motion
• Newton’s 3rd Law– For every action, there is
an equal and opposite reaction
Newton’s Third Law of Motion
Newton’s 3 Laws of Motion
• Newton's Laws of Motion
Momentum
• Momentum– Property of moving objects– Product of the object’s
mass and velocity– Momentum (p) = m x v– Linear Momentum
Law of Conservation of Momentum
• Law of Conservation of Momentum– Momentum of objects
do not change unless mass, velocity, or both change
– Momentum can be transferred from object to object