Forces, Motion, and Energy

Flashcards covering key concepts of motion, Newton's three laws, non-contact forces and fields, potential and kinetic energy, heat transfer mechanisms, and specific heat.

In science, what is the key difference between speed and velocity?

Speed is distance divided by time and indicates how fast something moves without direction, whereas velocity is speed in a specific direction (such as $60\,\text{km/h}$ north).

Why is a car traveling around a bend at a steady $60\,\text{km/h}$ considered to be accelerating?

Acceleration is how quickly velocity changes; even though the car's speed remains steady, its direction is changing, which means its velocity is changing.

On a distance–time graph, what do a flat line and a curved line represent?

A flat line means the object is not moving, while a curved line means the speed is changing, indicating that the object is accelerating.

On a distance–time graph, what does a steeper straight sloping line indicate compared to a less steep one?

A steeper line indicates a faster steady speed.

What does Newton's First Law state, and what is this property called?

An object keeps doing what it is doing (a stationary object stays still, and a moving object keeps moving at the same speed and direction) until a force acts on it; this property is called inertia.

What is the formula for Newton's Second Law, and how do net force and mass affect acceleration?

The formula is $a = F \div m$. Acceleration equals net force divided by mass; increasing the net force increases acceleration, while increasing the mass decreases acceleration.

What does Newton's Third Law state regarding forces?

Every force comes in a pair: whenever you push on something, it pushes back on you just as hard in the opposite direction.

What are the two forces that form Newton's Third Law pair when you stand on the floor?

You push down on the floor, and the floor pushes up on you.

How do seatbelts and airbags save lives during a collision based on force and stopping time?

They cause your body to stop over a longer time, and a longer stopping time results in a smaller force exerted on your body.

Which three forces can act across a gap without the objects touching?

Electric force, magnetic force, and gravitational force (gravity).

What is one important difference between gravity and electric or magnetic forces?

Gravity only ever pulls objects together, whereas electric and magnetic forces can both push apart (repel) and pull together (attract).

What is a field in science, and what provides visual evidence of a magnetic field?

A field is the region or space around an object where its force can be felt; iron filings placed on paper over a magnet line up in curved patterns, showing the shape of the magnetic field.

How do potential energy and kinetic energy change as a ball rolls down a ramp?

At the top, the energy is all potential energy; as it rolls down, potential energy transforms into kinetic energy until it is all kinetic energy at the bottom, while the total energy remains constant.

How does doubling an object's speed affect its kinetic energy compared to doubling its mass?

Doubling the mass doubles the kinetic energy, but doubling the speed makes the kinetic energy four times bigger.

According to the law of conservation of energy, what does it mean if an object's kinetic energy changes?

Energy must have moved into the object (if it speeds up) or out of the object (if it slows down, usually transferring to friction and heat), because energy is never created or destroyed.

In what direction does thermal (heat) energy always move?

Thermal energy always moves from hotter to colder.

How does radiation differ from conduction and convection as a method of heat transfer?

Radiation transfers heat via waves and can travel through empty space, whereas conduction requires direct contact and convection requires the physical movement of a liquid or gas.

How does a vacuum flask block all three forms of heat transfer to keep liquids hot?

It contains a gap with no air to prevent conduction and convection, and it has a shiny silver surface to reflect radiation back inside.

What is specific heat?

Specific heat is the amount of energy needed to raise the temperature of a material.

What three factors determine how much an object's temperature changes when heated?

How much energy is added, how much mass there is, and what the material is made of.

Why do coastal areas near the sea experience milder weather than inland areas?

Water has a high specific heat, meaning it heats slowly and cools slowly, allowing the sea to keep the temperature steady.