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Today in #PHY201 #GenPhys1: Review for the third midterm, which covers work, energy, momentum, and center of mass. Lots of conservation of energy and momentum questions!
November 2, 2026 at 10:08 PM
thomaswong.net
Yesterday in #PHY201 #GenPhys1: In a 1D elastic collision with two objects, relative velocity is reversed. When an object stops slowly, its impulse is the same, but the collision time is long, so the average force is less. This is how airbags protect people in accidents.
October 29, 2026 at 5:36 PM
thomaswong.net
Today in #PHY201 #GenPhys1: A net force acting for some time changes an object's mass times velocity, or momentum. For an isolated system, momentum is conserved. In a collision, mechanical energy is often not conserved, but momentum is.
October 26, 2026 at 8:06 PM
thomaswong.net
Today in #PHY201 #GenPhys1: Potential energy is the negative work done by a conservative force. Gravitational and spring are examples. Initial energy, plus work done by non-conservative forces, equals final energy.
October 21, 2026 at 5:48 PM
thomaswong.net
Today in #PHY201 #GenPhys1: The net work done on an object changes its kinetic energy. The work done by a conservative force does not depend on the path taken. Gravity is a conservative force, while friction is non-conservative.
October 19, 2026 at 7:28 PM
thomaswong.net
Yesterday in #PHY201 #GenPhys1: A box is moved some distance by several forces, including yours (F). The work you did is the component of your force along the direction of movement (Fcosθ), times the distance. Your perpendicular component (Fsinθ) didn't contribute to the work.
October 9, 2026 at 4:16 AM
thomaswong.net
Today in #PHY201 #GenPhys1: Static friction has strength up to the coefficient of static friction (μₛ) times the normal force (N). Beyond that, it slips, and kinetic friction is μₖN. Objects in circular motion have centripetal acceleration.
October 2, 2026 at 5:10 PM
thomaswong.net
Lately in #PHY201 #GenPhys1: Applications of Newton's 2nd Law involving the normal force, inclines, multiple objects, and tension.
September 30, 2026 at 7:49 PM
thomaswong.net
Today in #PHY201 #GenPhys1: Near the surface of the earth, the force of gravity is mg, which is weight. Objects resting on a surface experience a normal force perpendicular to the surface, and it could be equal to, greater than, or less than the weight depending on the situation.
September 23, 2026 at 4:55 PM
thomaswong.net
Today in #PHY201 #GenPhys1: The first exam, covering units, 1D kinematics, vectors, and 2D kinematics.
September 22, 2026 at 10:10 PM
thomaswong.net
Today in #PHY201 #GenPhys1: Newton's laws.
1st: In inertial ref frames, objects with zero net force don't accelerate.
2nd: Net force equals mass times acceleration.
3rd: If you push or pull on something, it pushes or pulls back with the same force, but the opposite direction.
September 16, 2026 at 10:09 PM
thomaswong.net
Today in #PHY201 #GenPhys1: If I drive in a circle at a constant speed, my velocity is changing because my direction is changing. So, I have an acceleration--centripetal acceleration--that points toward the center of the circle, even though I'm not speeding up or slowing down.
September 14, 2026 at 6:26 PM
thomaswong.net
Today in #PHY201 #GenPhys1: In projectile motion, there is constant velocity in the x-direction (with two equations) and constant acceleration in the y-direction (with four equations).
September 9, 2026 at 7:46 PM
thomaswong.net
Today in #PHY201 #GenPhys1: Ignoring air resistance, objects near the surface of the earth feel an acceleration due to gravity of -9.8 m/s^2, regardless of the mass of the object. This is constant acceleration, so we can use the kinematic equations for such "free fall" problems.
September 2, 2026 at 4:43 PM
thomaswong.net
Today in #PHY201 #GenPhys1: Acceleration is the rate of change of velocity. Assuming acceleration is constant, we derived four kinematic equations which have different combinations of variables.
August 31, 2026 at 7:13 PM
thomaswong.net
Today in #PHY201 #GenPhys1: If I walk 2 m right and 3 m left, how far did I travel? Two possible answers:
(1) 5 m is distance, a scalar.
(2) -1 m is displacement, a vector.
Velocity is the slope of a position vs time graph, and speed its magnitude.
August 26, 2026 at 4:13 PM
thomaswong.net
Today in #PHY201 #GenPhys1: We will use SI units, which are the same anywhere in the universe. The second is defined by the frequency of light to excite electrons in cesium atoms, the meter by the speed of light, and kilogram by the energy of photons.
August 24, 2026 at 7:49 PM
thomaswong.net
First day of #PHY201 #GenPhys1: Course introduction, about me, and each student. Almost every student needs the course for medical school, dental school, physical therapy school, or some other professional program. Then a math assessment to help students brush up.
August 19, 2026 at 7:32 PM
thomaswong.net
Happy New (School) Year! This semester, I'm teaching:
1. Quantum Physics and Technology for Everyone #PHY131 #QuantumForEveryone
2. General Physics for the Life Sciences 1 #PHY201 #GenPhys1
3. Quantum Mechanics #PHY531 #QuantumMechanics
August 18, 2026 at 7:02 PM