Imagine a universe where the force of gravity

  • Slides: 38
Download presentation
Imagine a universe where the force of gravity is repulsive, not attractive as it

Imagine a universe where the force of gravity is repulsive, not attractive as it is in our universe. What would that universe be like?

It would be like this, only without the stars. Everything would be hydrogen gas.

It would be like this, only without the stars. Everything would be hydrogen gas.

Ok, what would the universe be like if gravity was attractive, but was billions

Ok, what would the universe be like if gravity was attractive, but was billions of billions times stronger?

Much flatter than pancakes!

Much flatter than pancakes!

Now, what would the universe look like if there existed a force, that was

Now, what would the universe look like if there existed a force, that was both repulsive and attractive, and trillions of times stronger than gravity?

It would look like this! We call such a force the Electric Force

It would look like this! We call such a force the Electric Force

Science knows of four forces that exist in nature. The Strong Force The Weak

Science knows of four forces that exist in nature. The Strong Force The Weak Force. The Electromagnetic Force Gravity The strong and weak forces are short range forces, that is, they only act over very small distances (like inside the nucleus of an atom). Gravity and the electromagnetic forces are long range forces and can act over very large distances.

Perhaps the most startling thing about the electric force is how strong it is

Perhaps the most startling thing about the electric force is how strong it is compared to gravity It is approximately 3 x 1047 times stronger than gravity. Actually, it’s not that the electric force is so strong, it’s that gravity is so weak.

Rules of Electrostatics 1. There are two kinds of charge that exist in nature

Rules of Electrostatics 1. There are two kinds of charge that exist in nature (positive charge and negative charge) • unlike charges attract one another • like charges repel one another.

2. The force between charges varies as the inverse square of the distance, and

2. The force between charges varies as the inverse square of the distance, and directly with the charges. (Coulomb’s Law) 3. Charge is conserved. 4. Charge is quantized. (quantized means small discrete packets that can not be further subdivided. For example, you can have 1 or 2 electrons, but never 1. 5 electrons)

The basic unit of positive charge is the proton. (Although protons are ultimately made

The basic unit of positive charge is the proton. (Although protons are ultimately made up of quarks) The basic unit of negative charge is the electron. It is almost always electrons that are moving when charge “flows” The SI unit of charge is the Coulomb ( C). Charge of 1 e- = 1 proton = 1. 6 x 10 -19 Coulombs

Picture Time:

Picture Time:

Q

Q

Lisa rubs a piece of fur on glass rod, giving the rod a negative

Lisa rubs a piece of fur on glass rod, giving the rod a negative charge. What is the most likely thing that happens? 1) Protons are removed from the rod 2) Electrons are added to the rod 3) The fur is also charged negatively 4) The fur is left neutral

Lisa rubs a piece of fur on glass rod, giving the rod a negative

Lisa rubs a piece of fur on glass rod, giving the rod a negative charge. What is the most likely thing that happens? 1) Protons are removed from the rod 2) Electrons are added to the rod 3) The fur is also charged negatively 4) The fur is left neutral

Conductors & Insulators Conductors are materials in which charges are free to move. Metals

Conductors & Insulators Conductors are materials in which charges are free to move. Metals are a good example. Insulators are materials in which charges can not move. Glass, plastics, and wood, are examples. Q

Which of the following best characterizes electrical conductors? 1) Low mass density 2) High

Which of the following best characterizes electrical conductors? 1) Low mass density 2) High tensile strength 2) 3) Poor heat conductors 3) 5) All of the above 4) charges move freely

Which of the following best characterizes electrical conductors? 1) Low mass density 2) High

Which of the following best characterizes electrical conductors? 1) Low mass density 2) High tensile strength 2) 3) Poor heat conductors 3) 5) All of the above 4) charges move freely

Consider the “pith” ball… - +- -+ + ++ +- Charges are balanced, so

Consider the “pith” ball… - +- -+ + ++ +- Charges are balanced, so the ball is neutral

Consider the “pith” ball… - -- - + + + -

Consider the “pith” ball… - -- - + + + -

Consider the “pith” ball… - -- - - + - ++ -- +

Consider the “pith” ball… - -- - - + - ++ -- +

Consider the electroscope

Consider the electroscope

Consider the electroscope + ++

Consider the electroscope + ++

Consider the electroscope + ++ ++ + + + Explain what happens in pictures

Consider the electroscope + ++ ++ + + + Explain what happens in pictures & words Charging by conduction—A physical transfer of charge

Consider the electroscope + + + Be ready to explain what happens in pictures

Consider the electroscope + + + Be ready to explain what happens in pictures & words Charging by Induction

Consider the electroscope + + ++ + + + -- - -- + ++

Consider the electroscope + + ++ + + + -- - -- + ++ + + Charging by Induction Still neutral

Consider the electroscope + + ++ + + + -- - -- + ++

Consider the electroscope + + ++ + + + -- - -- + ++ + + Charging by Induction

Consider the electroscope + + ++ + + + -- - -- These charges

Consider the electroscope + + ++ + + + -- - -- These charges flow from the ground to the electroscope. - - + + + - - ++ + + Charging by Induction These charges remain held in place

Consider the electroscope + + ++ + + + -- - -- The electroscope

Consider the electroscope + + ++ + + + -- - -- The electroscope is now charged. - - - Charging by Induction - Explain what happens in pictures & words These charges now spread out.

Q

Q

An uncharged conductor is supported by an insulating stand. I pass a positively charged

An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be… 1) Negative 2) Positive 3) Neutral 5) Depends on the materials. 4) Attracted

An uncharged conductor is supported by an insulating stand. I pass a positively charged

An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be… 1) Negative 2) Positive 3) Neutral 5) Depends on the materials. 4) Attracted

An uncharged conductor is supported by an insulating stand. I pass a positively charged

An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be… 1) Negative 2) Positive 3) Neutral 5) Depends on the materials. + + ++ +++ - - -- + ++ + + 4) Attracted