AP Physics C: Mechanics College Board

This subject is broken down into 19 topics in 7 modules:

  1. Gravitation 2 topics
  2. Kinematics 2 topics
  3. Newton's Laws of Motion 3 topics
  4. Oscillations 1 topics
  5. Rotation 4 topics
  6. Systems of Particles and Linear Momentum 3 topics
  7. Work, Energy and Power 4 topics
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  • 7
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  • 19
    topics
  • 7,258
    words of revision content
  • 56+
    minutes of audio lessons

This page was last modified on 28 September 2024.

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Physics C: Mechanics

Gravitation

Gravitational Forces

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Gravitational Forces

Gravitational Forces

Key Terms

  • Gravity: A force of attraction between all mass, particularly evident between large bodies such as the Earth and Moon.
  • Mass: The amount of matter in an object. Immune to changes in volume or density.
  • Weight: The force of gravity acting on a mass. Changes with the strength of the gravitational field.
  • Gravitational field strength (g): The force of gravity per unit mass at a point in a gravitational field.

Newton's Law of Universal Gravitation

  • Every object in the universe attracts every other object with a force directed along the line of centres for the two objects.
  • This force is proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between the centres of the two objects.
  • The mathematical representation is: F = G(m1 * m2) / r^2
    • F is the force of gravity (measured in newtons)
    • G is the gravitational constant
    • m1 and m2 are the masses of the objects
    • r is the distance between the centres of the two objects

Gravitation and Weight

  • An object’s weight refers to the force with which it is pulled toward the centre of the Earth due to gravity.
  • The weight can be calculated using W = mg, where:
    • W is weight (measured in newtons)
    • m is the mass of the object (measured in kilograms)
    • g is the gravitational field strength (measured in N/kg)
  • On Earth, g is approximately 9.81 N/kg. Therefore, an object with a mass of 1 kg has a weight of 9.81 N on Earth.

Gravitational Field Strength

  • Gravitational field strength is the force of gravity per unit mass.
  • It varies based on location, being strongest at the surface of an object and decreasing as you move further away.
  • The formula to compute gravitational field strength is: g = F/m, where:
    • g is the gravitational field strength (measured in N/kg)
    • F is the gravitational force (measured in newtons)
    • m is the mass of the object experiencing the force (measured in kilograms)

Importance of Understanding Gravitational Forces

  • Gravitational forces are fundamental to many aspects of everyday life and scientific study, from how objects fall to the ground to the prediction of planetary orbits.
  • Understanding gravity and its effects can help solve real-world problems, such as the construction of buildings and bridges, and it also forms the basis for exploring other areas of physics, such as relativity.

Course material for Physics C: Mechanics, module Gravitation, topic Gravitational Forces

Physics C: Mechanics

Rotation

Rotational Kinematics

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Rotational Kinematics

Understanding Rotational Kinematics

  • Rotational kinematics is about studying the motion of objects rotating about a fixed axis.
  • It contains similar elements to linear kinematics, but these elements get adapted to fit rotational motion.
  • Just as we have distance, velocity, and acceleration in linear motion, we have angular displacement, angular velocity, and angular acceleration in rotational motion.

Key Concepts in Rotational Kinematics

  • Angular displacement states the angle through which an object rotates. It is measured in radians and can be calculated using the radius times the angle in radians.
  • Angular velocity is the rate of change of angular displacement and is denoted as ω. It also represents the speed at which the object rotates.
  • Angular acceleration denotes the rate of change of angular velocity, symbolized as α.

Formulas and Equations of Motion for Rotational Kinematics

  • The basic equation of motion links angular displacement, initial angular velocity, angular acceleration and time: θ = ω0t + 0.5αt².
  • Angular velocity can be found with the formula ω = ω0 + αt.
  • The angular displacement can also be calculated using θ = 0.5(ω + ω0)t.
  • Angular velocity squared can be found via ω² = ω0² + 2αθ.

The Importance of Radians in Rotational Kinematics

  • Angular measurements in rotational kinematics are often in radians rather than degrees.
  • This is because radians provide a direct correlation between a circle's radius and its circumference, which facilitates calculations.

Rotational Kinematics in Real-Life Situations

  • Applications of rotational kinematics can be observed in various real-world scenarios such as turning wheels of vehicles, spinning turbines, and more.
  • Understanding these principles can help you solve complex problems that involve rotating objects and predict their future positions based on their existing state of motion.

Practising Questions Involving Rotational Kinematics

  • It's beneficial to practice problems involving rotational kinematics, such as finding the angular velocity of a spinning wheel or calculating the angular displacement of a turning gear over time.
  • Work through examples using the key formulas and principles, reinforcing your understanding of the concept.

Consolidating your understanding of rotational kinematics will equip you to tackle problems involving rotational motion with confidence and accuracy.

Course material for Physics C: Mechanics, module Rotation, topic Rotational Kinematics

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