Fundamental Laws of Physics: Units 1-3
Unit 1: Newton’s Laws of Motion
Newton’s First Law (Law of Inertia)
An object in motion stays in motion unless acted upon by an unbalanced outside force. For example, a ball sitting on a table will not move until someone hits it.
- Distance: Total movement.
- Displacement: Direct line movement (change in position).
Newton’s Second Law
F = ma (Force equals mass times acceleration). A wooden ball moves faster in space than a brass ball.
Newton’s Third Law
For every action, there is an equal but opposite reaction. For example, Newton’s Cradle demonstrates this principle.
Key Concepts
- Position: Where an object is located in relation to a reference point.
- Reference Point: A single comparison.
- Frame of Reference: A collection of comparisons.
- Scalars: Have only magnitude (e.g., mass, temperature, speed, distance).
- Vectors: Have both magnitude and direction (e.g., position, velocity, force, displacement).
Gravity and Free Fall
- Gravity: g = -9.8 m/s2
- Up or to the right is positive (+).
- Down or to the left is negative (-).
- Objects in Free Fall: Initial velocity (Vi) = 0 m/s.
Everyday Forces and Free Body Diagrams
Everyday Forces
- Fapp (Applied Force): Force applied by humans, in whatever direction.
- Fg (Gravitational Force): Always downwards.
- FN (Normal Force): “Contact” force, perpendicular to the surface.
- Ff (Frictional Force): Parallel to the surface, opposite to the direction of motion.
- Ft (Tensional Force): Along the rope or string, away from the object.
- Fs (Spring Force): Along the spring, a restorative force.
Free Body Diagrams
- Balanced Forces: No acceleration.
- Unbalanced Forces: Acceleration (the longest arrow wins).
- Used to visualize the forces acting on an object.
- Can conceptually confirm a problem or situation.
- Can help predict acceleration.
Four Fundamental Forces
- Strong Nuclear: Holds the nucleus together.
- Weak Nuclear: Responsible for radioactive decay.
- Electromagnetic: Involves electric charges and magnets.
- Gravity: Attractive force over a distance.
- Weak + Electromagnetic = Electroweak.
One-Dimensional Motion: Single movement (left or right).
Two-Dimensional Motion: Two movements (left or right, then up or down).
Weightlessness: Occurs during free fall (no forces other than gravity and normal force).
Motion with no acceleration: Yes, an object can move at a constant speed without acceleration.
Unit 2: Work, Energy, and Power
Key Formulas and Concepts
- k: Spring constant (N/m).
- x: Distance stretched.
- EA = EB
- Force: Measured in Newtons.
- Work: Measured in Joules.
- Displacement: Measured in meters.
- Power: Measured in Watts.
- PEe & KE: Measured in Joules.
Relationships
- Work is affected by distance and force.
- Power is affected by work, time, and speed.
- Power: The rate at which work is done.
- Kinetic Energy (KE): Velocity has a greater effect.
- Gravitational Potential Energy (PEg): Mass and height affect it equally.
- Energy Transfer: Energy is exchanged or transferred between objects.
- Energy Transformations: Energy changes forms from one type to another.
Energy
What is energy? The ability to do work.
Types of Energy:
- Kinetic: Motion, thermal, sound, electromagnetic, electric.
- Potential: Gravitational, nuclear, chemical, elastic.
Simple Machines
Wheel and axle, screw, pulley, lever, wedge, gear.
Unit 3: Momentum and Collisions
Important Details for Describing Collisions
Velocity, speed, momentum, force, time, mass.
Momentum
p = mv (“Mass in Motion”, measured in kg*m/s). All objects have mass, but not all have momentum. More movement equals more momentum. Since velocity has direction, so does momentum. Momentum can change in a collision but is not affected by an object’s position.
Impulse
Change in momentum (measured in Ns). F = m(ᇫv/t). Unchanged in a collision.
Types of Collisions
- Elastic Collisions: Two objects bounce apart. Momentum and KE are conserved.
- Inelastic Collisions: Two objects stick together (real-life scenarios). Momentum is conserved, but KE is not.
Note: Energy is conserved, but KE is transformed into sound and heat.
Angular Momentum
Depends on mass, velocity, and the radius of the spinning mass. L = mvr.
Collision Examples
Scenario 1: A red car hits a stationary blue car with velocity (v). The red car is twice as massive as the blue car. The red car will travel at a slower velocity than it started with.
Scenario 2: A blue car traveling with some speed hits a red car traveling with the same speed in the opposite direction. The blue and red cars are equally as massive. They will become stationary.
Magnitude of Impulse
Determined by force and time.
Formulas
m1(v1) + m2(v2) = m1(v1a) + m2(v2a)
m1(v1) + m2(v2) = m1+2(v1+2)