Modern Physics

Forces Inside the Nucleus

The strong nuclear force, electrostatic repulsion, fusion, and fission

Forces Inside the Nucleus lesson illustration

 

What is the name of the nuclear reaction that occurs in the sun?

 

Forces Inside the Nucleus lesson illustration

 

"Why don't the

protons in a nucleus

fly apart?"

Don't likes repel?"

 

cassiopeiaproject.com

School Blocks YouTube? Use the file below.

| Fission_and_Fusion |

 

 

 

Forces Inside the Nucleus lesson illustration 

"How can you possibly
learn about the parts of a nucleus when it's so small that you can't
even see it with
a microscope?"

 

Forces Inside Nucleus

 

1) Strong Nuclear Force

(A.K.A. 'strong force')

 

• Holds Nucleus Together - very strong, short range

 

• operates at distance < 10-13 m

 

 

Two H nuclei fuse into a single helium atom.
What is this nuclear reaction called?

Forces Inside the Nucleus lesson illustration

wpclipart.com

 

 

 

 

Fusion - Uniting of small nuclei
 to form a larger nuclei

 

 

 


Our sun is large fusion 'bomb'.

Forces Inside the Nucleus lesson illustration

wpclipart.com

 

 

Forces Inside the Nucleus lesson illustration

A is for Atom

School Blocks YouTube? Use the file below.

BingEnergyFission.mp4

This movie is part of the collection: Prelinger Archives

Producer: Sutherland (John) Productions Sponsor: 
General Electric Company

Keywords: Atomic-nuclear: Energy; Physics; Animation

Creative Commons license: Public Domain

 

 

A) Binding Energy - amount of energy needed to separate nucleons (protons and neutrons) in nucleus.

 

 

Protons and neutrons in nucleus in large nuclei have slightly less mass than n and p in small nuclei

 

 

Mass of Assembled
Nucleus

<

Combined Mass of an
 Equivalent # of Nucleons.

 

 


Lost Mass
called Mass Defect

 

 

Mass Defect
  =
Binding Energy

(mass lost is
converted to energy)

 

 

Ex) If the mass defect is .1 universal mass units then the binding energy = ....

 

(p. 1 Reference)

 

1 Universal Mass Unit

converts to

 

9.31 x 102 Mev

(p. 1 ref)

 

 

9.31 x 101 Mev

 

 
Stable lead-208 nucleus beside an unstable radium-226 nucleus that decays into radon-222, releasing an alpha particle and energy; heating, cooling, dissolving, or sealing the sample does not change the decay rate NYSSLS Reading Passage icon

NYSSLS Reading Passage · Modern Physics

Glowing in the Dark: Marie Curie and the Atom That Wouldn't Sit Still

Open Reading Passage → Regents Practice Version →
Marie Curie illustration

🎧 Podcast · 21 min

Marie Curie’s Radioactive Notebooks

More episodes →

Explore: When a Nucleus Is Unstable

Unstable nuclei change by giving off radiation.

Pick a starting nucleus and press a decay button. Watch the protons, neutrons, and notation change.

Try This

Start with Ra-226 (the radium on this page) and press Alpha. What does it become?

↓

It becomes radon-222: the mass number drops by 4 and the atomic number drops by 2.

More: Nuclear Physics lessons

Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. Why don't the protons in a nucleus fly apart despite repelling each other?

2. Which describes the strong nuclear force?

3. Two hydrogen nuclei join to form helium, as in the Sun. This reaction is called…

4. A nucleus has a mass defect of 0.1 universal mass units. What is its binding energy? (1 u = 931 MeV)

5. Why does an assembled nucleus have less mass than its separate protons and neutrons?

NYSSLS Regents Practice · Modern Physics · Fundamental Forces

What Holds the Nucleus Together?

A helium-4 nucleus contains two protons and two neutrons packed into a space about 10−15 m across. At that distance, the two protons repel each other with an electrostatic force of roughly 230 N — enormous for such tiny particles.

Why doesn’t the nucleus fly apart?

▶ Want a challenge? Open 6 more Regents-style questions  (harder · mixed formats)

Challenge score: 0 / 6

Substitute values

C1. Substitute numerical values into a mathematical representation that can be used to determine the electrostatic force between the two protons when they are 1.0 × 10−15 m apart. Then calculate the force. (k = 8.99 × 109 N·m2/C2; e = 1.60 × 10−19 C)

Fe = (8.99 × 109 N·m2/C2)( × 10−19 C)2( × 10−15 m)2 = N
Multiple choice

C2. What is a key property of the strong nuclear force?

Support or Refute · Justify

C3. A student makes the following claim.

Claim: The gravitational attraction between the two protons (m = 1.67 × 10−27 kg each) is strong enough to balance their electric repulsion.

Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship. (G = 6.67 × 10−11 N·m2/kg2)

Draw the vector · Determine the magnitude

C4. Two protons lie on a horizontal line, 2.0 × 10−15 m apart. Consider only the electrostatic force. Choose the direction of the electrostatic force on the proton on the right, and determine its magnitude.

right proton
●
Fe = N
Multiple choice

C5. How do neutrons help stabilize large nuclei?

Constructed response

C6. Very large nuclei, such as uranium-238 (92 protons), are unstable. Using the different ranges of the strong nuclear force and the electrostatic force, explain why adding more protons to a large nucleus makes it less stable.

Subatomic Particles →

Also see: The Big Bang — evidence for the origin of the universe

Also see: Nuclear Physics — radioactive decay, fission, and fusion