# Newton¢â‚¬â„¢s Laws of Motion - SFSU Physics & jfielder/ ¢  Newton¢â‚¬â„¢s Laws of Motion

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Isaac Newton (1642-1727)

• English physicist and mathematician

• Studied motion, light, and gravity

Newton puts all the pieces together

Newton’s Law of Gravity

• Key idea: Mass • Mass is _________________________

– NOT the same as _____ (to a scientist) – You can be weightless, but never mass-

less

Newton’s Law of Gravity

• Everything with mass pulls on everything else with mass

• Gravity is always _________ • The _____ the object, the ______ the

pull

Newton’s Law of Gravity

F = -G × (Mm/r2)

• M = • m = • r = • G = gravitational constant

= 6.67 × 10-11 m3/s2kg

M

m

r

Newton’s Law of Gravity

F = -G × (Mm/r2)

• Force grows or shrinks with ________ ________ – If you get 2x closer, force is __x _______ – If you get 3x farther away, force is __x

_______ • Called Inverse-square relation

Newton’s Laws of Motion #1: A body continues at rest or in uniform motion in a

straight line unless ______ _____ ___ ___ _____.

Why doesn’t the soccer ball move on its own?

What causes a soccer ball to roll to a stop on the grass?

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Newton’s Laws of Motion #2: The amount of change in a body’s motion is

proportional to the force acting on it, and along the same direction as the force.

F (_____) = m (____) × a (___________)

If I kick the ball this way

________________ ______________

If I kick the ball harder,

____________

The more _______ the body, the more _____ you need to

change its motion

Need ________ force to move a bowling ball

Only need _______ force to move a ping-pong ball

Newton’s Laws of Motion

#3: When one body exerts a force on a second body, the second body exerts an _____ and ________ force back on the first body.

What’s happening at the moment

when I kick the soccer ball?

Hint: Think about what would happen if you kicked the ball really hard with no shoes on.

Gravity Lecture Tutorial: Pages 29-31

• Work with a partner or two • Read directions and answer all questions carefully.

Take time to understand it now! • Come to a consensus answer you all agree on before

moving on to the next question. • If you get stuck, ask another group for help. • If you get really stuck, raise your hand and I will

come around.

The Moon and Earth pull on each other with _____ strength

and in _______ directions

Earth

Moon

Fg Fg

You and Earth pull on each other with _____ strength and

in _________ directions

Earth

Fg

Fg

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Wait, I thought I understood this stuff! Shouldn’t Earth feel less gravity from me? I’ve got

a lot less mass than Earth!

The more massive the body, the more force you need to change its motion

Earth

Fg

Fg

Which one will move more: You or Earth?

a (acceleration) = F (force) m (mass)

Light and Matter: Reading Messages from the

Cosmos How do we experience light?

• The warmth of sunlight tells us that light is a form of ______

• We can measure the ______, or flow of energy over time, of light in units of ______

• One _____ is about the amount of power used to lift an apple over your head in 1 second

_____ of Light

• White light is made up of many different _____

How do light and matter interact?

• Emission • Absorption • Transmission

– Transparent objects let light through – Opaque objects block or absorb light

• Reflection or Scattering

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Reflection and Scattering Interactions of Light withMatter

What is light?

• Light can act either like a ____ or like a ________

• Particles of light are called _________

Waves

A wave is a pattern of motion that can carry _____ without carrying _____ along with it

Properties of Waves

• ___________ is the distance between two wave peaks

• _________ is the number of times per second that a wave vibrates up and down

____ ______ = wavelength x frequency

Light: Electromagnetic Waves

• A light wave is a _______ of electric and magnetic fields

• Light interacts with charged particles through these electric and magnetic fields

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Wavelength and Frequency

wavelength x frequency = ______ __ _____ = _________

Particles of Light

• Particles of light are called photons • Each photon has a _________ and a

__________ • The energy of a photon depends on its

frequency

Wavelength, Frequency, and Energy

λ x f = c λ = , f = c = 3.00 x 108 m/s = speed of light

E = h x f = photon energy h = 6.626 x 10-34 joule x s = Plank’s constant

What is the electromagnetic spectrum?

What is the electromagnetic spectrum? Gamma Rays •____ ____ frequency

•____ ____ energy

•Damaging to humans!

•Can only be studied from space

•Gamma ray bursts, nuclear reactions

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X-rays

•Still pretty high ______

•Medical uses

•Can still only be studied from ______

•Gas in galaxy clusters, supernova remnants, or the Sun’s corona

Ultraviolet (UV) Light

•Getting closer to visible light!

•Too much is still a bad thing (____________)

•Visible in supernova remnants and coming from very hot stars

Visible Light

•Light our ____ ___ ___!

•Wavelengths about as long as bacteria

•Produced in stars

Infrared (IR) Light •__ _____ in IR light!

•Beyond the range of human sight

•____-_____ _______

•Given off by planets, some gas clouds, and moons

•Very wide range of wavelengths / frequencies

•Subcategories: __, __, __, _______, _______

•The CMB (cosmic microwave background) glows in microwaves

EM Spectrum Lecture Tutorial: Pages 45-47

• Work with a partner or two • Read directions and answer all questions carefully.

Take time to understand it now! • Come to a consensus answer you all agree on before

moving on to the next question. • If you get stuck, ask another group for help. • If you get really stuck, raise your hand and I will

come around.

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