Chapter 2 Forces and motion

Think about it…. If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit the ground first? Would it matter if the cliff were very high or particularly low? How could Mr. Coyote slow down his fall?

Section : Gravity and Motion LEFT Section : Gravity and Motion Gravity and Falling Objects - Activity Gravity and Acceleration Demo 1: Which will hit the ground first, second, third, a basketball, baseball, ping pong ball? Prediction: Observation:

Acceleration Due To Gravity RIGHT - NOTES Acceleration Due To Gravity Acceleration = the rate of velocity changing over time. A falling object accelerates at a constant rate. The object falls farther and faster each second than it did the second before

Velocity of Falling Objects RIGHT - NOTES Velocity of Falling Objects Table of Formulas Equation: V = g x t Example Problems: EX 1: A penny at rest is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen for 2 s?      EX 2: The same penny hits the ground in 4.5s. What is the penny’s velocity as it hits the ground?

Velocity of Falling Objects EX 3: A marble at rest is dropped from a tall building. The marble hits the ground with a velocity of 98 m/s. How long was the marble in the air? EX 4: An acorn at rest falls from an oak tree. The acorn hits the ground with a velocity of 14.6 m/s. How long did it take the acorn to land?

Air Resistance and Falling Objects Demo Air Resistance and Falling Objects Demo1: Which falls faster? Crumpled paper or flat sheet of paper? Why did this happen?

Activity - LEFT Falling Water Trial 1 Observation: Trial 2 Observation: What differences did you observe in the behavior of water during the two trials? In trial 2, how fast did the cup fall compared with how fast the water fell?

Spider Map Activity - LEFT 9.8 m/s2 force gravity Opposes gravity Forces and Motion force Air resistance Constant velocity Projectile Motion Terminal velocity Gravity = air resistance Object accelerates vertically downward Objects in curved path Centripetal force Free Fall Unbalanced force No air resistance Objects in circular path Object moves forward Only gravity orbiting Object in free fall

Spider Map Activity - LEFT 9.8 m/s2 force gravity Opposes gravity Forces and Motion force Air resistance Constant velocity Terminal velocity Gravity = air resistance Free Fall No air resistance Only gravity

Air Resistance and Falling Objects RIGHT - NOTES Air Resistance and Falling Objects Air Resistance - force that opposes the motion of objects through air

Acceleration Stops at Terminal Velocity RIGHT - NOTES Acceleration Stops at Terminal Velocity As the speed of a falling object , air resistance . Air resistance until it = gravity. Terminal velocity – the constant velocity of a falling object when the air resistance = gravity An Introduction to Skydiving

Free Fall Occurs When There Is No Air Resistance RIGHT - NOTES Free Fall Occurs When There Is No Air Resistance Free fall – the motion of a body when only the force of gravity acts it Two places that have no air resistance and free fall: Vacuum Space

Orbiting Objects are in Free Fall RIGHT - NOTES Orbiting Objects are in Free Fall An object is in orbit for two reasons: It is moving forward It is in free fall LEFT - PICTURE

Orbiting and Centripetal Force RIGHT - NOTES Orbiting and Centripetal Force Centripetal force - the unbalanced force that causes objects to move in a circular path Ex. The moon orbits the earth, the earth around sun Space exploration: What is an orbit? The swing set myth

Projectile Motion and Gravity RIGHT - NOTES Projectile Motion and Gravity Projectile Motion and Gravity Projectile Motion- the curved path that an object follows when thrown. Horizontal Motion - When you throw a ball, the forward force your hand exerts on the ball Vertical Motion- Pulled down towards the earth by gravity LEFT - PICTURE

Quick lab – penny projectile motion LEFT - ACTIVITY Quick lab – penny projectile motion Position a ruler and two pennies on a desk. Hold the ruler by the end on the desk, move the ruler quickly so it knocks the penny off the table and so that the other penny also drops. Repeat. Which penny travels in a projectile motion? In what order do the pennies hit the ground?

seCTION 2: Newton’s Laws of Motion RIGHT - NOTES seCTION 2: Newton’s Laws of Motion Newton’s First Law of Motion An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force. What does this mean? This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

Newton’s first law of motion LEFT - PICTURE Newton’s first law of motion What is the motion in this picture? Forward motion – rolling What is the unbalanced force in this picture? Rock What happened to the skater in this picture? Fall off the skateboard What other force do you know that can stop an object from moving? Friction, gravity

Newton’s first law of motion RIGHT - NOTES Newton’s first law of motion Newton’s 1st Law is also the reason you wear a seatbelt! Newton’s 1st Law is also known as inertia Inertia – the tendency of an object to resist being moved, or if the object is moving to resist a change in speed or direction until an outside force acts on it Does mass have an affect on inertia? Yes mass has an affect on inertia Would you rather catch a baseball or bowling ball?

LEFT - PICTURE Exploring inertia

Newton’s Second Law of Motion Acceleration is produced when a force acts on a mass. The greater the mass, the greater the force needed to accelerate the object. So, Heavier objects need more force to move the same distance as lighter objects

Newton’s 2nd Law of Motion Newton’s 2nd Law can be expressed as a mathematical equation: or FORCE = MASS times ACCELERATION SI Unit for force = Newtons (N)

Newton’s 2nd law of motion Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s2. Using Newton's Second Law, you can compute how much force Mike is applying to the car.

Newton’s 2nd law of motion What is the acceleration of a 3 Kg mass if a force of 14.4 N is used to move the mass? What force is necessary to accelerate a 1,250 Kg car at a rate of 40 m/s2?

RIGHT - NOTES Newton’s third law For every action there is an equal and opposite re-action. …When an object pushes another object it gets pushed back in the opposite direction equally hard …For every force there is a reaction force that is equal in size, but opposite in direction.

RIGHT - NOTES Newton’s third law Action – rocket pushes down on the ground with the force of its engines Reaction - the ground pushes the rocket up with an equal force. Newton’s Cradle

Section 3: Momentum p = m x v RIGHT - NOTES Section 3: Momentum Momentum - Depends on the object’s mass and velocity. The more momentum an object has, the harder it is to stop the object or change directions. Momentum = mass x velocity p = m x v (Kg m/s) (Kg) (m/s) What would have more momentum? A bowling ball or a basketball rolled at the same velocity? Bowling ball b/c it has more mass   A tractor trailer or a Honda civic at the same velocity? Tractor trailer

Momentum p = m x v Momentum = mass x velocity (Kg m/s) (Kg) (m/s) RIGHT - NOTES Momentum Momentum = mass x velocity p = m x v (Kg m/s) (Kg) (m/s) Example: A 100 Kg car falls off a cliff from rest and hits the ground with a velocity of 35 m/s. What is the car’s momentum when it hits the ground? A 35 Kg bowling ball was thrown at Tommy at a velocity of 15 m/s. What was the bowling ball’s momentum?

RIGHT - NOTES Momentum Problems What is the momentum of an ostrich with a mass of 120 Kg that runs with a velocity of 16 m/s north? What is the momentum of a 6 Kg cat that is moving at 10 m/s down the alley toward the mouse? An 85 Kg man is jogging with a velocity of 2.6 m/s to the north. Nearby, a 65 Kg person is skateboarding and is traveling with a velocity of 3 m/s north. Which person has a greater momentum? Show your work.

Section 3: Momentum Momentum and Velocity and Mass RIGHT - NOTES Section 3: Momentum Momentum and Velocity and Mass If you increase velocity, then momentum increases If you increase mass, then momentum increases Collisions If a moving train collides with a train at rest and the trains move together, you momentum of both is equal If a heavy object (bowling ball) collides with a light object (bowling pin), the heavy object’s momentum decreases

law of conservation of momentum RIGHT - NOTES law of conservation of momentum When two objects collide, their combined momentum remains the same after collision Newton’s third law of motion = Conservation of Momentum   5 Reaction Force Action Force The action force is the cue ball, the reaction force is the #5 billiard ball exerting force back  

Concept MAP – Gravity Review LEFT - DRAW Concept MAP – Gravity Review Gravity