Physics Flashcards

A student observes that increasing the mass of an object increases the force needed to move it. What scientific law best explains this?

Answer: Newton's Second Law

Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F=ma). Therefore, if the mass (m) of an object increases, a greater force (F) is required to produce the same acceleration (a), explaining why more force is needed to move a heavier object.

A ball is thrown straight up. What is the direction of its acceleration at the top of its path?

Answer: Downward

At the very top of its path, when a ball is thrown straight up, its instantaneous vertical velocity is zero, but it is still under the influence of gravity. The force of gravity continuously pulls the ball downward, resulting in a constant downward acceleration (approximately 9.8 m/s² on Earth), which causes it to fall back down.

Why does a metal spoon feel colder than a wooden spoon at the same room temperature?

Answer: Metal is a better conductor of heat

Metal feels colder than wood at the same room temperature because metal is a much better thermal conductor. When you touch the metal spoon, heat rapidly transfers from your warmer hand to the colder metal, causing your hand to lose heat quickly and perceive the metal as cold, whereas wood, being an insulator, transfers heat much slower.

If you double the velocity of an object, what happens to its kinetic energy?

Answer: It quadruples

Kinetic energy (KE) is calculated using the formula KE = 0.5 * m * v², where m is mass and v is velocity. If you double the velocity (2v), the new kinetic energy becomes 0.5 * m * (2v)² = 0.5 * m * 4v² = 4 * (0.5 * m * v²). Therefore, doubling the velocity quadruples the kinetic energy.

Which situation best demonstrates the law of conservation of momentum?

Answer: Two skaters push off each other and roll away

The law of conservation of momentum states that in a closed system, the total momentum remains constant. When two skaters push off each other, they exert equal and opposite forces (Newton's Third Law), resulting in equal and opposite changes in their individual momenta, but the total momentum of the two-skater system before and after the push remains conserved.

What type of energy is stored in a compressed spring?

Answer: Elastic potential energy

Elastic potential energy is the energy stored in an elastic material, such as a spring, when it is deformed (stretched or compressed) from its equilibrium position. This stored energy has the potential to do work and will be converted into kinetic energy when the spring is released.

A mirror reflects light to form a clear image. Which principle does this demonstrate?

Answer: Reflection

Reflection is the phenomenon where light waves bounce off a surface, such as a mirror, and return into the same medium. A clear image is formed because the light rays reflect in a predictable and organized manner, following the law of reflection, allowing our eyes to perceive the reflected image.

What happens to the current in a circuit if the resistance increases while voltage stays the same?

Answer: Current decreases

According to Ohm's Law, which states V = IR (Voltage = Current x Resistance), current and resistance are inversely proportional when voltage is constant. Therefore, if the resistance in a circuit increases while the voltage remains the same, the current flowing through the circuit must decrease to maintain the equality.

Why does a helium balloon rise in air?

Answer: It is lighter than air

A helium balloon rises because helium gas is less dense than the surrounding air. According to Archimedes' principle, an object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced. Since the helium balloon displaces a volume of air that weighs more than the balloon itself (including the helium), it experiences a net upward force, causing it to rise.