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