Vesta, the second largest object in the asteroid belt, was recently imaged for the first time by the robotic Dawn satellite that arrived last month.

Homework #2 short answers due Wednesday, 2:30 pm multiple choice deadline Thursday, 11:00 pm The first exam has been shifted from Monday, September 26 to Monday, October 3.

Scalars and Vectors Scalar: a quantity described solely by its size (and units) Vector: a quantity described by its size AND direction

speed – rate at which an object moves [e.g., m/s]. A scalar quantity. velocity – an object’s speed AND direction, [e.g.,10 m/s east]. A vector quantity. acceleration – a change in an object’s velocity, i.e., a change in speed OR direction [m/s 2 ]. A vector quantity.

Momentum (p) – the mass of an object times its velocity (p=mv) Force (f) – anything that can cause a change in an object’s momentum As long as the object’s mass does not change, a force causes a change in velocity, or an acceleration (a) Force, momentum, and acceleration are all vectors

Newton’s First Law of Motion A body in motion remains in motion and a body at rest remains at rest unless acted upon by an outside force. If the net force acting on an object is zero, then there is no change in the object’s motion. OR

The change in a body’s velocity due to an applied force is in the same direction as the force, and is proportional to the force, but is inversely proportional to the body’s mass. F = ma Or F = rate of change of momentum Newton’s Second Law of Motion

Forces only affect motion in the direction of the force.

A planet is always changing its direction of motion. Newton’s second law therefore states that a force must be acting on the planet. Gravity provides this force. Gravity & Orbits Motion without an applied force gravity

F = ma can be rewritten to show that for a given force, the acceleration is inversely proportional to the mass: a = F / m

Least mass Most mass Intermediate mass a = F / m

Do not confuse mass and density Mass = amount of matter Density = amount of matter per volume Higher density means more matter packed into same volume

Law of Conservation of Momentum If the net force (sum of all external forces) acting on an object is zero, then the total momentum of a system remains constant. Momentum: p = mv

Newton’s Third Law of Motion “For every applied force, a force of equal size but opposite direction arises” or For every action there is an equal and opposite reaction

A Universe of Matter and Energy What is matter? What is energy?

Matter – material such as rocks, water, air; “stuff” composed of atoms Energy – makes or has the potential to make matter move! The history of the universe, including biological organisms, is based upon the interplay between matter and energy.

Three Basic Types of Energy kinetic – energy of motion potential – stored energy; e.g., chemical, gravitational, electrical, etc. radiative – energy transported by light (electromagetic radiation)

Conservation of Energy  Fundamental law of nature  Energy can be neither created nor destroyed  It can change form or be exchanged between objects.  The total energy content of the Universe was determined in the Big Bang and remains the same today. K.E. P.E.R.E.

Kinetic Energy (K.E.): energy of motion K.E. = 1/2 mv 2 (m is mass, v is velocity)

On the microscopic level: temperature is a measure of the AVERAGE kinetic energy of particles within a substance

Temperature Scales

Temperature vs. Heat ● Temperature is the average kinetic energy. ● Heat (thermal energy) is the total kinetic energy. lower Thigher T same T less heatmore heat

Sound waves are a form of kinetic energy on a microscopic level (organized vibration of molecules)

Applying what we’ve learned - pizza vs. soup caution in the kitchen

Potential Energy: Energy that is “stored” within an object and that has the potential of being released in a different form

Gravitational Potential Energy ● gravitational potential energy is the energy which an object stores due to its ability to fall ● It depends on: – the object’s mass (m) – the strength of gravity (g) – the distance which it can fall (d) m d g ● P.E. = mgd

● gravitational potential energy g ● P.E. = mgd

Mass-Energy Potential Energy ● mass-energy: energy is stored in matter itself ● this mass-energy is what would be released if an amount of mass, m, were converted into energy E = mc 2 [ c = 3 x 10 8 m/s is the speed of light]

Chemical Potential Energy ● Chemical potential energy: energy stored chemical bounds

There are many additional examples of potential energy. e.g., stretched springs, …

Energy, while conserved, can be transformed from one type of energy to another Potential Kinetic

Kinetic Potential

Orbits & Energy Maximum Kinetic Energy Maximum Potential Energy Downhill Uphill

From the perspective of energy, which planet is more difficult to reach from the Earth? Mars Venus

From the perspective of energy, which planet is more difficult to reach from the Earth? Mars It is “uphill”

ConceptTest The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size … (yellow) stays the same (red) slowing changes into other forms of energy (green) slowly increases (blue) interstellar clouds do not have gravitational potential energy

ConceptTest The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size … (yellow) stays the same (red) slowing changes into other forms of energy (green) slowly increases (blue) interstellar clouds do not have gravitational potential energy

ConceptTest In the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is … (yellow) likely to be true (red) false (green) difficult to determine if this will happen or not. (blue) this has already happened, but the government is suppressing this discovery.

ConceptTest In the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is … (yellow) likely to be true (red) false (green) difficult to determine if this will happen or not. (blue) this has already happened, but the government is suppressing this discovery.