- Review oscillations and energy - Look again at the energy stored in a “spring” - Begin a final review of force, motion and energy concepts - Repeat the sun plot analysis for new data TODAY’S OUTCOMES: FORCE, MOTION AND ENERGY THE SUN AND MOON

A) Describe the role that the friction force plays in this game. A game you can play is to give a penny a shove so that it slides across a table, trying to get it to stop on a target. Friction is the force that acts on the penny opposite the direction of motion, and accelerates it to an eventual stop. B) Assume that the penny is sliding on the table with a known speed. Explain how friction and the laws of motion determine how far the penny goes before it stops. C) Assume that the penny is sliding on the table with a known speed. Explain how the energy concept explains how far the penny goes before it stops. 1st Law: The penny keeps moving until friction applies a force 2nd Law: Friction applies a force to accelerate the penny 3rd Law: The penny exerts a force back on your finger The penny begins with a certain amount of kinetic energy - the energy supplied by friction to stop the penny must equal the initial kinetic energy. D) The mass of a penny is kg. If the initial velocity is 0.5 m/sec and the sliding friction force = N, how far does the penny slide? Kinetic energy = 1/2 mv 2 = 0.5 × kg × 0.5 m/s × 0.5 m/s = Joules Joules = Force × distance distance = J/0.004 N = 0.25 m

OSCILLATIONS Oscillations can be looked at in terms of force and acceleration, or in terms of energy.

OSCILLATIONS Pendulum: Force and Acceleration tension weight weight and tension are NOT equal and opposite here, so there is a net force, and thus an ACCELERATION net force

OSCILLATIONS Pendulum: Force and Acceleration tension weight At the bottom, tension and weight cancel - no net force

OSCILLATIONS Pendulum: Force and Acceleration on the swing upward, forces become unbalanced again, net force reappears tension weight net force Acceleration in a pendulum is always toward the central line, or equilibrium position (where it would hang if stationary.)

OSCILLATIONS Pendulum: Energy Potential energy is stored as pendulum is pulled back; there is no motion or kinetic energy yet

OSCILLATIONS Pendulum: Energy At the bottom, the potential energy is gone - but speed and kinetic energy are highest

OSCILLATIONS Pendulum: Energy on the swing upward, the speed and kinetic energy lower; potential energy is again stored

OSCILLATIONS SPRING: Force and acceleration “restoring” force pull from hand When the spring is “pulled back”, the pull from your hand and the restoring force are balanced equilibrium line

OSCILLATIONS SPRING: Force and acceleration “restoring” force When you release, you remove the force from your hand - forces are no longer balanced - restoring force = the net force net force SPRING ACCELERATES UP

OSCILLATIONS SPRING: Force and acceleration When the spring returns to equilibrium position, it is MOVING quickly, but there is no more restoring force; NO ACCELERATION at this instant no net force

OSCILLATIONS SPRING: Force and acceleration “restoring” force When the spring passes the equilibrium line, the restoring force pulls the other way net force SPRING ACCELERATES DOWN

OSCILLATIONS SPRING: Energy When the spring is pulled down, POTENTIAL ENERGY is stored in the spring

OSCILLATIONS SPRING: Energy As the spring passes the equilibrium, there is no more potential energy; but the speed is maximum, along with kinetic energy

OSCILLATIONS SPRING: Energy As the spring reaches the other side, it slows, and kinetic energy again becomes potential energy

MASS OF SPRING vs. PENDULUM SPRING Mass increases, restoring force stays same; so acceleration decreases Frequency decreases with mass PENDULUM Mass increases, restoring force (weight) also increases, so acceleration stays the same Frequency does not depend on mass

- Understand how to view pendulums and springs in terms of force, acceleration and energy - How pendulum and spring periods vary with mass and amplitude - How to measure frequency (frequency = 1 / period) WHAT YOU ARE EXPECTED TO KNOW:

- Review oscillations and energy ✓ - Look again at the energy stored in a “spring” - Begin a final review of force, motion and energy concepts - Repeat the sun plot analysis for new data TODAY’S OUTCOMES: FORCE, MOTION AND ENERGY THE SUN AND MOON