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ap physics 1
👉 AP Physics Essentials
👟 Unit 1 - Kinematics
1.1Position, Velocity, and Acceleration
🌀 Unit 2 - Dynamics
2.5Newton's Third Law and Free-Body Diagrams
🚀 Unit 3 - Circular Motion
3.0Unit 3 Overview: Circular Motion and Gravitation
3.3Gravitational and Electric Forces
3.4Gravitational Field/Acceleration Due to Gravity on Different Planets
3.5Inertial vs. Gravitational Mass
3.7Free-Body Diagrams for Objects in Uniform Circular Motion
⚡️ Unit 4 - Energy
4.1Open and Closed Systems: Energy
4.2Work and Mechanical Energy
⛳️ Unit 5 - Momentum
🎸 Unit 6 - Simple Harmonic Motion
6.1Period of Simple Harmonic Oscillators
🎡 Unit 7 - Torque & Rotational Motion
7.2Torque and Angular Acceleration
7.3Angular Momentum and Torque
💡 Unit 8 - Electric Charges & Electric Force
8.0Unit 8 Overview: Electric Charge and Electric Force
8.1Conservation of Charge
🔋 Unit 9 - DC Circuits
9.1Definition of a Circuit
9.3Ohm’s Law, Kirchhoff’s Loop Rule (Resistors in Series and Parallel)
🔊 Unit 10 - Mechanical Waves & Sound
10.1Properties of Waves
10.3Interference and Superposition (Waves in Tubes and on Strings)
✍️ Free Response Questions (FRQs)
Paragraph Length Response
⏱️ 1 min read
May 31, 2020
A closed system refers to a system that doesn’t lose mass, energy, charge, etc so conserved quantities are considered to be constant. On the other hand, an open system refers to exchanges of energy, charge, etc with the object(s) surroundings.
Open systems may seem to violate conservation of mass, charge, matter, and energy since the amount of the previously stated quantities can increase or decrease without replacement.
Image Credit: physics.usyd.edu
In terms of momentum of a system, internal forces, like all forces, always occur in action reaction pairs. Since the forces in action reaction pairs are equal and opposite due to Newton’s 3rd law, internal forces must always sum to zero. If the internal forces cancel, that means that the sum of the total forces must simply be all of the external forces. External forces could sum to zero but that won’t always be the case.
The change in net momentum is directly related to the net external force. If the net external force acting on a system is equal to zero, then its net momentum is conserved so pinitial = pfinal. This only applies to the net momentum of a system, not individual momenta of each object.
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