8th Grade Science Final

Newton’s Third Law

• For every action, there is an equal and opposite reaction.

• Forces always come in pairs: equal in strength, opposite in direction.

• These forces act on different objects.

• Example: You push a wall → the wall pushes back equally.

Effects of Forces on Motion

• Unbalanced forces change motion (speed or direction).

• Balanced forces = no change in motion.

• More mass = more force needed to change motion.

Electromagnetic Forces

• Can be attractive or repulsive.

• Opposite charges attract; like charges repel.

• Strength depends on charge, current, magnet strength, and distance.

Forces Acting at a Distance

• Gravity, electric, and magnetic forces act over a distance.

• These forces work through fields.

• Gravitational fields affect mass.

• Electric fields affect charge.

• Magnetic fields affect magnets and currents.

Potential Energy in Systems

• Stored energy due to position.

• Higher position = more gravitational potential energy.

• Example: Book on a high shelf vs. floor.

Interaction & Energy Transfer

• When two objects interact, energy can transfer.

• Example: Moving car hits parked car → energy transfers.

• Energy is not lost, just transferred or transformed.

Changes in Motion Energy

• Motion energy changes when other energies change too.

• Example: Falling object changes potential to kinetic energy.

• Energy is always conserved (transferred or transformed).

Understanding Celestial Patterns

• We use models to explain movement of sun, moon, and stars.

• Phases of the moon follow a ~29.5-day cycle.

• Earth’s rotation causes day/night; revolution causes seasons.

Causes of Seasons

• Caused by the tilt of Earth's axis.

• Earth gets different sunlight angles during its orbit.

Earth’s Galaxy

• Earth is in the Milky Way galaxy, a spiral galaxy.

• Our solar system orbits the galaxy’s center.

Formation of Solar System

• Formed from a spinning disk of gas and dust.

• Gravity pulled material together → formed sun and planets.

• This took millions of years.

Ecosystem Dynamics

• Ecosystems change due to natural or human causes.

• One disruption can affect many populations.

• Example: Pollution or introducing a new species.

Natural Selection

• Traits that help survival/reproduction become more common.

• Caused by environmental pressures.

• Example: Long necks help giraffes reach food → more survive.

Adaptation & Evolution

• Helpful traits become more common over generations.

• Changes in DNA (mutations) can lead to adaptations.

• This process = evolution.

Anatomical Similarities

• Similar body parts suggest a common ancestor.

• Example: Limb bones in humans, whales, and bats are similar.

Geologic Time Scale

• Organizes Earth’s history using rock layers and fossils.

• Law of Superposition: Deeper layers = older.

• Time is divided into eons, eras, periods, and epochs.

Simple Waves

• Have repeating patterns: wavelength, frequency, amplitude.

• Wavelength = peak to peak.

• Amplitude = height from rest to peak.

• Frequency = how often waves pass.

Transmission of Sound Waves

• Sound waves need a medium (like air, water, solids).

• Sound can’t travel in a vacuum.

Light Interaction

• Light can be reflected, absorbed, or transmitted.

• Depends on object material and light frequency.

• Mirrors reflect; black objects absorb; clear objects transmit.

Digitized Signals

• Digital signals are more reliable than analog.

• Less interference; better for sending info.

• Used in phones, internet, etc.

Human Impact on Climate

• Humans release greenhouse gases like CO₂.

• This traps heat → causes global warming.

• Main cause: burning fossil fuels.

Goal of Science

• To understand natural events through evidence and testing.

• Results must be reproducible by others.

Adaptation

• A trait that helps an organism survive and reproduce.

• Can be physical, behavioral, or internal.

• Example: Camouflage or hibernation.

Natural vs. Artificial Selection

• Natural: happens in nature; survival-based.

• Artificial: humans choose traits (like dog breeding).

• Both involve passing traits to offspring.