General Science
Physics & Mechanics
Physics explains how matter, forces, motion, and energy behave. For General Science, focus on forces, mass and weight, gravity, Newton's laws, friction, momentum, energy, machines, pressure, buoyancy, sound, and basic light behavior. This is a conceptual lesson, not a calculation-heavy physics course.
Section 1
Force, Mass, Weight & Gravity
A force is a push or pull that can start or stop motion, change speed or direction, or change shape. Mass is the amount of matter in an object. Weight is the force of gravity acting on that mass.
An astronaut has the same mass on Earth and the Moon but weighs less on the Moon because its gravity is weaker. Gravity is an attractive force between masses; near Earth it pulls objects toward the planet.
Example 1
An astronaut travels from Earth to the Moon. Which quantity remains essentially the same? A. Weight | B. Mass | C. Gravitational pull | D. Force of gravity
Solution
- 1The astronaut still contains the same amount of matter.
- 2The Moon's weaker gravity changes weight, not mass.
Why: Mass measures matter, while weight depends on gravity.
Example 2
What causes an unsupported object near Earth's surface to fall? A. Magnetism | B. Gravity | C. Friction | D. Sound
Solution
- 1Earth's gravity pulls objects toward its center.
Why: Gravity causes falling objects to accelerate downward near Earth.
Section 2
Newton's Laws of Motion
Newton's laws describe how forces affect motion. The first law is inertia: an object keeps its state of motion unless an unbalanced force acts. The second law is F = ma. The third law states that forces occur in equal and opposite pairs.
For the same force, a smaller mass accelerates more than a larger mass. If mass stays the same, more force produces more acceleration. A swimmer pushes water backward, and water pushes the swimmer forward.
Example 1
A passenger moves forward when a car suddenly stops. Which concept explains this? A. Inertia | B. Buoyancy | C. Pressure | D. Density
Solution
- 1The passenger was moving with the car.
- 2When the car stops, the body tends to keep moving until another force acts.
Why: Newton's First Law describes this tendency to remain in motion.
Example 2
Two carts receive the same force. Cart A has much less mass than Cart B. Which accelerates more? A. Cart A | B. Cart B | C. Both equally | D. Neither
Solution
- 1Use F = ma conceptually.
- 2For the same force, smaller mass produces greater acceleration.
Why: Less mass requires less force to produce the same acceleration.
Example 3
A person jumps from a small boat toward a dock and the boat moves backward. Which law explains this? A. First | B. Second | C. Third | D. Conservation of mass
Solution
- 1The person pushes backward on the boat while moving forward.
- 2The boat experiences an opposite force.
Why: Forces occur in equal and opposite pairs.
Section 3
Friction, Momentum & Center of Gravity
Friction resists motion between surfaces in contact. It provides useful grip for shoes, tires, and brakes, but can also cause heat, wear, and reduced efficiency.
Momentum describes how difficult it is to stop a moving object and depends on mass and velocity. The center of gravity is where an object's weight can be considered concentrated. A lower center of gravity and a wider base generally make an object more stable.
Example 1
Why are tire treads useful on a wet road? A. They reduce friction to zero. | B. They help maintain friction. | C. They increase mass. | D. They lower air pressure.
Solution
- 1A vehicle needs tire-road friction to accelerate, turn, and stop.
Why: Without enough friction, tires slide instead of gripping.
Example 2
Which object generally has greater momentum? A. Slowly moving tennis ball | B. Fast-moving truck | C. Stationary truck | D. Empty cup at rest
Solution
- 1Momentum depends on mass and motion.
- 2A fast-moving truck has high mass and high speed.
Why: Greater mass and speed generally mean greater momentum.
Example 3
Which design is more difficult to tip? A. High center and narrow base | B. Low center and wide base | C. High center and tall shape | D. Narrow base only
Solution
- 1A low center of gravity and wide base increase stability.
Why: The weight remains more securely over the base of support.
Section 4
Work, Energy & Power
Energy is the ability to do work. In physics, work occurs when a force moves an object through distance: work = force × distance. Power describes how quickly work is done.
Kinetic energy is energy of motion. Potential energy is stored energy, such as an object raised above ground or a compressed spring. A falling object changes gravitational potential energy into kinetic energy.
Example 1
A ball is held at the top of a hill. What energy does it have because of position? A. Gravitational potential | B. Sound | C. Chemical reaction only | D. Electrical current
Solution
- 1The elevated position gives the ball stored energy.
Why: Gravitational potential energy depends on position in a gravitational field.
Example 2
As a ball rolls downhill and speeds up, what energy change occurs? A. Kinetic to all potential | B. Potential to kinetic | C. Energy disappears | D. Mass to sound
Solution
- 1As the ball loses height, gravitational potential energy decreases.
- 2Its motion increases.
Why: Stored gravitational energy converts to energy of motion.
Example 3
Two workers lift identical boxes to the same height. A takes 5 seconds and B takes 10. Who uses greater power? A. A | B. B | C. Both zero | D. Power cannot depend on time
Solution
- 1Both perform about the same work.
- 2A completes it in less time.
Why: Power measures how quickly work is performed.
Section 5
Simple Machines & Mechanical Advantage
Simple machines change the force, direction, or distance involved in work. They do not create free energy. The six basic machines are lever, pulley, wheel and axle, inclined plane, wedge, and screw.
A lever is a rigid bar around a fulcrum. A pulley uses a wheel and rope. An inclined plane is a ramp. A wedge splits or cuts. A screw is an inclined plane wrapped around a cylinder. Mechanical advantage reduces input force, often by requiring force over a greater distance.
Example 1
Why does a ramp make raising a heavy object easier? A. It eliminates gravity. | B. It allows smaller force over longer distance. | C. It reduces mass. | D. It creates energy.
Solution
- 1A ramp is an inclined plane.
- 2It trades greater distance for reduced required force.
Why: Simple machines reduce force needed but do not eliminate total work.
Example 2
What is the fixed pivot point of a lever called? A. Fulcrum | B. Axle | C. Wedge | D. Pulley
Solution
- 1A lever rotates around a fixed point.
Why: The fulcrum is the pivot around which a lever moves.
Example 3
Which simple machine is an axe blade? A. Pulley | B. Wedge | C. Wheel and axle | D. Lever only
Solution
- 1An axe blade pushes material apart as it moves through it.
Why: A wedge converts force into forces that separate or cut material.
Section 6
Pressure & Buoyancy
Pressure describes force distributed over area: pressure = force / area. The same force over a smaller area produces more pressure. Liquids and gases exert pressure as fluids.
Liquid pressure generally increases with depth because more liquid is above. Buoyancy is an upward fluid force on an object. Objects tend to float when buoyant force can balance weight, and lower average density than the fluid also helps floating.
Example 1
Why can a sharp needle pierce material more easily than a blunt object with the same force? A. Less pressure | B. Force over smaller area | C. No mass | D. Gravity disappears
Solution
- 1Pressure is force divided by area.
- 2A small contact area creates greater pressure.
Why: The same force over smaller area makes greater pressure.
Example 2
In a large body of water, where is pressure generally greater? A. Near surface | B. Greater depth | C. Always zero | D. Only outside water
Solution
- 1At greater depth, more water is above the object.
Why: The fluid above contributes to greater pressure.
Example 3
What force pushes upward on an object in water? A. Friction | B. Buoyant force | C. Magnetic force | D. Tension only
Solution
- 1Fluids exert an upward buoyant force.
Why: Buoyancy opposes some or all of an object's downward weight in a fluid.
Section 7
Sound
Sound is produced by vibrations that travel through a medium as waves. It can travel through solids, liquids, and gases, but not a perfect vacuum because no particles are present to carry vibration.
Frequency is related to pitch: higher frequency means higher pitch. Amplitude is related to loudness. Sound generally travels faster through solids than gases because particles are closer together.
Example 1
What causes sound? A. Vibrations | B. Gravity alone | C. Chemical bonds breaking only | D. Static mass
Solution
- 1Sound begins when matter vibrates.
Why: Vibration makes surrounding particles vibrate and transfer a sound wave.
Example 2
Which change produces a higher-pitched sound? A. Lower frequency | B. Higher frequency | C. Lower gravity | D. Greater mass only
Solution
- 1Pitch is directly related to frequency.
Why: Faster vibration frequencies are perceived as higher pitches.
Example 3
Why can sound not travel through a perfect vacuum? A. It needs particles to transfer vibrations. | B. Gravity is too strong. | C. Light blocks sound. | D. It becomes heat.
Solution
- 1Sound is a mechanical wave and requires matter through which vibrations can move.
Why: A vacuum has no medium to carry the sound wave.
Section 8
Basic Light Concepts
Light is electromagnetic energy and can travel through a vacuum. Reflection is light bouncing off a surface. Refraction is light bending when it moves between materials.
Transparent materials allow most light through clearly; translucent materials allow some through but scatter it; opaque materials do not allow light through. Objects appear different colors because they reflect some visible wavelengths more than others.
Example 1
A pencil appears bent when partly in water. What causes this? A. Refraction | B. Buoyancy | C. Friction | D. Inertia
Solution
- 1Light changes direction when moving between air and water.
Why: Refraction is bending of light between materials.
Example 2
Which material allows most visible light to pass through clearly? A. Opaque | B. Transparent | C. Dense only | D. Magnetic
Solution
- 1Transparent materials transmit most visible light clearly.
Why: Objects on the other side can be seen clearly through transparent material.
Quick Review
Quick Review
- Force is a push or pull. Mass is matter; weight is gravity acting on mass. Newton's First Law is inertia, Second Law is F = ma, and Third Law is equal and opposite pairs.
- Friction opposes motion; momentum depends on mass and velocity; potential energy is stored and kinetic energy is motion.
- Simple machines trade force for distance. Pressure = force / area. Buoyancy is upward fluid force. Sound requires a medium; light does not.
The Big Picture
- More force → greater acceleration when mass is constant. More mass → less acceleration for the same force. Greater height → more gravitational potential energy. Smaller contact area → greater pressure. Higher sound frequency → higher pitch. Light changing materials may refract.