GRAVITIONAL FIELDS
Page 1: Introduction to Gravitational Fields
Gravitational Fields: Force fields associated with gravitational interaction explained.
Force fields are a concept beyond science fiction.
Page 2: Fundamental Forces
The Four Fundamental Forces
Gravity
Strength: Infinite range
Particle: Graviton (?); mass = 0, spin = 2
Electromagnetic Force
Strength: Infinite range
Particle: Photon; mass = 0, spin = 1
Strong Nuclear Force
Strength: Very strong but short range (approx. diameter of a medium sized nucleus)
Particle: Gluons
Weak Nuclear Force
Strength: Short range (about 0.1% of the diameter of a proton)
Particles: Intermediate vector bosons (W+, W-, Z); mass > 80 GeV, spin = 1
Page 3: What is a “Force Field”?
Definition: A region where an object experiences a non-contact force due to its inherent nature.
Types of Force Fields:
Not all objects are magnetic.
Not all objects experience electric fields.
Gravitational fields require matter to experience its effects.
Page 4: Gravitational Field Concept
Einstein's Perspective: Gravitational fields seen as distortions in space-time.
Visualization: Analogy of a bowling ball on a rubber sheet, creating a dent that illustrates gravitational attraction.
Page 5: Properties of Gravitational Fields
Law of Attraction: All matter attracts other matter (Newton’s Third Law).
Gravitational Force:
Acts inwardly.
A 1 kg mass 1 meter apart experiences ~6.67 x 10^-11 N attraction.
On Earth, a 1 kg mass is acted on by a force of 9.8 N (gravitational field strength).
Formula for gravitational field: g = Fg / m (where g = 9.8 N/kg on Earth).
Changes in force with distance follow the inverse square law (increases/decreases with distance).
Page 6: Example of Weight Calculation
Problem: Determine mass of rock with a gravitational pull of 126 N on Earth.
Weight is the force that a planet exerts on another object measured in Newtons.
A distinction between weight (force) and mass (invariant)
Example: A 100 kg person exerts 980 N on Earth due to gravitational effects.
Page 7: Weight on Different Planets
Example: Lunar Module
Weight on the Moon: 21,900 N; gravitational field strength = 1.6 N/kg.
Weight on Venus: 19,700N; calculation of g on Venus required.
Page 8: Duck Dodgers Example
Duck Dodgers’ weight on Planet X determined by his mass (1.9 kg) and drop time (0.74 s) of an object from 1.0 m.
Page 9: Apparent Weight & Normal Force
Exploration of how perceived weight differs from actual weight based on conditions.
Page 10: Understanding Normal Force
Definition: The normal force acts when two surfaces are in contact.
Acts perpendicular to surfaces involved.
Page 11: Apparent Weight Explained
Definition: The weight we sense and feel through our legs; termed as the normal force.
Factors influencing apparent weight - affects experienced during activities like bungee jumping.
Page 14: Calculating Normal Force
Key Equations
FNET = ma
FNET = FN + Fg
Fg = m(9.8)
Example: Assess apparent weights during elevator acceleration phases.
Page 16: Friction Introduction
Definition: Frictional force opposing motion between two surfaces.
Page 18: Types of Friction
Kinetic Friction
Opposes sliding motion of two surfaces.
Static Friction
Prevents two surfaces from sliding against each other.
Static friction exhibits a threshold.
Page 19: Characteristics of Friction
Kinetic Friction is constant when surfaces remain unchanged; Static Friction has a maximum threshold.
Page 20: Factors Influencing Friction
Amount of normal force (FN) matters.
Coefficient of friction (μ) is crucial for friction determination:
μK: Coefficient of kinetic friction.
μS: Coefficient of static friction; μS > μK.
Page 23: Friction Example Problem 1
40 kg box on a surface with μS = 0.61 & μK = 0.21:
Pushing with different forces gives different friction types.
Page 24: Friction Example Problem 2
Assess box sliding at constant cinematic speed, then calculate distance based on kinetic friction coefficient.