CSET Physical Science: General Science Domain 2

Newtons Laws

• 1st Law 

  • An object stays at rest or keeps moving at constant velocity unless acted on by a net force.

  • More mass → more inertia.

• 2nd Law 

  • F = ma

  • More force → more acceleration

  • More mass → less acceleration for the same force

• 3rd Law

  • Every action force has an equal and opposite reaction force.

  • Forces act on different objects.

Forces & free-body diagrams

• Force = push or pull on an object

• Free-body diagram (FBD) = shows all forces acting on an object

• Represent forces with arrows

• Arrow direction = direction of force

• Longer arrow = greater force

  • Common forces:

    • Gravity ↓

    • Normal force ↑

    • Friction opposes motion

    • Tension along a rope/string

    • Applied force = push/pull

Net force

• Net force = total force acting on an object

• Forces in the same direction → add

• Forces in opposite directions → subtract

  • Net force = 0 → no acceleration

    • Object stays at rest or moves at constant velocity

  • Net force ≠ 0 → object accelerates

Vectors

• Scalar = magnitude only

  • Examples: speed, distance, mass, time

• Vector = magnitude + direction

  • Examples: velocity, displacement, acceleration, force

• Vector Addition

  • Same direction → add

  • Opposite directions → subtract

  • Direction of the larger vector determines the final direction

Pressure

• Pressure = force applied over an area

• Smaller area → greater pressure

• Larger area → less pressure

• Formula 

  • Pressure = Force / area 

Fluid flow & buoyancy

• Fluid flow 

  • Pressure = force per area

  • Fluids generally flow from higher pressure → lower pressure

  • Faster fluid flow → lower pressure (in many common fluid-flow situations)

• Buoyancy

  • Buoyant force = upward force a fluid exerts on an object

  • Object floats if buoyant force balances its weight

  • Object sinks if weight > buoyant force

  • Object is neutrally buoyant if forces balance while submerged

Fundamental forces

• There are 4 fundamental forces:

  • Gravity → attraction between masses

  • Electromagnetic → interactions between charged particles

  • Strong nuclear → holds the nucleus together

  • Weak nuclear → involved in radioactive decay

• Strong nuclear > Electromagnetic > Weak nuclear > Gravity

Mechanical vs. Electromagnetic Waves

• Mechanical waves 

  • Require a medium to travel

  • Examples: sound (vibrations), water waves, seismic waves

• Electromagnetic (EM) waves

  • Does not require a medium

  • Can travel through a vacuum (like space)

  • Examples: light, radio waves, X-rays

Transverse vs. Longitudinal Waves 

• Transverse Waves

  • Particles vibrate perpendicular to wave direction

  • Think: up and down while wave moves forward

  • Example: light, waves on a rope

• Longitudinal Waves

  • Particles vibrate parallel to wave direction

  • Creates compressions and rarefactions

  • Example: sound

Frequency, wavelength, amplitude

• Frequency

  • Number of waves that pass a point per second

    • Measured in Hz (hertz)

• Wavelength (λ)

  • Distance from one wave peak to the next

• Amplitude

  • Maximum displacement from the resting position

  • Related to wave energy/intensity

• Relationship

  • Higher frequency → shorter wavelength (if wave speed stays constant)

  • Lower frequency → longer wavelength

Wave energy

• Waves transfer energy from one place to another.

  • Amplitude → greater amplitude = more energy

  • Frequency → higher frequency generally means more energy for EM waves.

• The wave itself does not necessarily transport matter; particles usually just oscillate around their positions.

Reflection, Refraction, Transmission

• Reflection

  • Wave bounces back when it hits a surface

  • Example: echo, mirror

• Refraction

  • Wave changes direction when it enters a different medium

  • Happens because its speed changes

  • Example: light bending when it enters water

• Transmission

  • Wave passes through a material or boundary

  • Example: light passing through glass

• Reflection = bounces | Refraction = bends | Transmission = passes through

Resonance

• A physics phenomenon that occurs when an object or system is exposed to a vibrating force that matches its own natural frequency.

• This causes energy transfer to increase.

• Light & Lenses

• Light

  • Light is an electromagnetic wave

  • Can travel through a vacuum

  • Can be reflected, refracted, transmitted, or absorbed

• Lenses

  • Concave lens → thinner in the middle → diverges (spreads light rays apart)

  • Convex lens → thicker in the middle → converges (brings light rays together)

Kinetic & potential energy

• Kinetic energy (KE) = energy of motion

  • Faster object → more KE

  • More massive object → more KE

• Potential energy (PE) = stored energy

  • Gravitational PE depends on height and mass

  • Higher object → more gravitational PE

• Formulas

  • KE = ½mv²

  • PE = mgh

Electric charge

• The property of matter that causes electric forces.

• Two types: positive (+) and negative (−).

  • Like charges repel.

  • Opposite charges attract.

• Electrons = negative; protons = positive.

Electric fields

• A region around a charged object where another charge experiences a force.

• Field direction:

  • Away from positive charges

  • Toward negative charges

• Stronger charge → stronger electric field.

• Closer to the charge → stronger field.

Magnetic fields

• A region around a magnet where magnetic forces act.

• Magnetic field lines go from North → South outside a magnet.

  • Strongest magnetic field = near the poles.

• Moving electric charges (current) can create magnetic fields.

Electrostatic & Magnetostatic Phenomena + Examples

• Electrostatics (Stationary Charges):

  • Forces between electric charges that are not moving.

  • Key Mechanism: Friction, conduction, or induction separates electrons.

  • Examples: A rubbed balloon sticking to a wall, socks sticking together in a dryer, lightning, or plastic wrap clinging to a bowl.

• Magnetostatics (Steady Magnetic Fields):

  • Forces produced by magnetic materials or steady, unchanging electric currents.

  • Examples: A refrigerator magnet holding paper, a compass needle pointing north, or sorting scrap metal with a permanent magnet.

Relating Currents to Magnetic Fields & Applications

• Electromagnets: A wire coiled around an iron core. Turning the electric current on creates a temporary magnet. You can make it stronger by adding more coils or increasing the current.

• Electric Motors: Convert electrical energy → mechanical energy. Electric current passes through a loop inside a magnetic field, creating a magnetic force that forces the loop to spin.

• Generators: Convert mechanical energy → electrical energy. Spinning a wire loop inside a magnetic field forces electrons to move, generating an electric current (the exact opposite of a motor).

• Transformers: Devices that change voltage using two isolated coils. An alternating current in the primary coil creates a changing magnetic field, which induces a higher or lower voltage in the secondary coil.

• Voltage, Current, Resistance, and Electrical Power (Ohm’s Law)

• Voltage, current, resistance

  • Voltage (V) = electrical potential difference; the “push” that drives current.

  • Current (I) = flow of electric charge.

  • Resistance (R) = opposition to the flow of current.

  • Higher resistance → less current (if voltage stays the same).

• Formula

  • Ohm’s Law: V = IR

    • V = voltage

    • I = current

    • R = resistance

• Electrical power

  • Electrical power = rate at which electrical energy is used or transferred.

  • Measured in watts (W).

  • Higher power → more energy used per unit of time.

  • Formula

    • P = VI

      • P = power

      • V = voltage

      • I = current