Physics Forces and Interactions Quiz

CCC Scale, Proportion, and Quantity

• Force relevance changes across scales.
• Diagrams should show a distance scale from solar system to proton size, marking force relevance at different points.
• Noncontact (gravitational) forces are most relevant at the scale of the solar system.
• Contact forces (electromagnetic) are relevant at scales where objects interact on or within Earth.
• Relevance shifts to noncontact (nuclear) forces at atomic scales.

SEP Analyze and Interpret Data

• Apple's mass is 0.10 kg.
• Velocity data given for an apple falling from a tree.
• Plot a momentum graph using the provided data.
• Determine the force on the apple as it falls.
• Analyze if the force changes or remains constant.
• Check if the data supports Newton's second law of motion.
• Momentum graph should illustrate a steadily increasing momentum with a constant rate of acceleration.
• Constant net force is implied by the constant acceleration.
• Constant acceleration is a key requirement of Newton's second law.

SEP Construct an Explanation

• Weight is the force exerted by Earth on a mass.
• Newton's third law pair for weight is Earth and the mass.
• Both Earth and mass exert the same force magnitude on each other.
• Forces act in opposite directions.
• Weight is exerted at the center of mass.

SEP Plan an Investigation

• Measuring spring constant using five masses.
• The mass is the independent variable.
• Displacement of the spring is the dependent variable.
• Calculate spring force using weight calculation.
• Hooke's law is applied to calculate the spring constant.

Spring Constant Calculation

• Spring length is 0.30 m.
• Mass added is 0.50 kg.
• Stretched length is 0.32 m.
• Spring constant is 250 N/m.

Spring Stretch Calculation

• Spring constant is 10.0 N/m.
• Weight hung is 15 N.
• Spring stretch is 1.5m.

SEP Interpret Data

• Copper stretches more easily than steel.
• Suggests electric forces holding atoms together are weaker in copper than steel.

Types of Forces

• Diagram depicting 18 N and 44 N forces acting on a dog.

Objectives

• Analyze data to understand relationships between net force, mass, and acceleration.
• Apply Newton's laws to predict macroscopic object motion.

Forces Acting on a Sitting Person

• Several forces act on a person sitting at a desk.
• Gravitational force pulls downward.
• Normal force from the chair counteracts weight.
• Normal force from the desk supports arm weight (if resting).
• Friction between person and chair prevents sliding.

Contact and Noncontact Forces

• Contact force: interaction between objects in direct contact.
• Noncontact force: interaction between objects separated in distance.

Contact Forces (Examples)

• Rubbing hands
• Car skidding
• String holding a plant
• Guitar string vibrating
• Book on table
• Leaning against a wall
• Pushing a door
• Lifting a box

Noncontact Forces (Examples)

• Apple falling
• Moon orbiting Earth
• Charged balloon on wall
• Magnets attracting/repeling
• Strong force in atomic nucleus
• Energy released in nuclear reaction
• Roller coaster car
• Satellite orbiting Earth

Weight

• Weight is a downward force due to Earth's gravity.
• Measured in Newtons.
• Weight = mass x acceleration due to gravity (W=mg).

Effect of Earth's Mass on Weight

• Increased Earth mass leads to greater gravitational attraction, meaning increased weight. Decreased Earth mass leads to less gravitational attraction, meaning decreased weight.

Weight Calculation Examples

• 100 kg mass on Earth weighs 980 N.
• 100 kg mass on the moon weighs 160 N.

Spring Force

• Spring's deformation is proportional to the applied force.
• Spring constant determines resistance to deformation (Hooke's Law).
• F = -kx, where k is the spring constant.

Effect of Spring Constant on Flexibility

• Lower spring constant implies easier pulling and compression.

Negative Sign in Hooke's Law

• Negative sign indicates spring force opposes the applied force, pulling to return to original position when released.

Tension

• Tension is the pulling force along a rope, cable or chain.
• Tension is a contact force.
• Electric forces are a non-contact force between electrically charged objects.

Surface Forces

• Surface forces involve spring-like interactions between surfaces in contact.
• Friction is the parallel component of surface force.
• Static friction acts on objects at rest, while kinetic friction acts on moving objects).
• Coefficient of friction quantifies resistance between surfaces.

Modeling Force in Two Dimensions

• Vector components of forces in defined coordinate systems.
• Applying forces in multiple directions.

Centripetal Force

• Centripetal force causes circular motion. Directed toward the center of motion.
• Fc = mv²/r (centripetal force = mass × velocity² / radius).

Moon's "Falling"

• Moon is continually pulled toward Earth by gravity.
• This force provides centripetal acceleration required for orbital motion.
• Without the pull of gravity, the moon would travel in a straight line.