Gravity
Isaac Newton • 1665 under an apple tree
Gravity • Isaac Newton • Two questions? • Why do things fall to the Earth? • Why do the planets stay in motion?
Gravity • Gravity • The force of attraction between two bodies • All matter has mass, therefore all matter has gravity
Gravity • The Law of Universal Gravitation • Gravitational force increases as mass increases • Gravitational force decreases as distance increases
The Law of Universal Gravitation • Gravitational force increases as mass increases • Gravitational force decreases as distance increases 10N 100N 10N 100N
The Law of Universal Gravitation • Gravitational force increases as mass increases • Gravitational force decreases as distance increases 10N 10N 10N 10N
Gravity • Gravity and Motion • Galileo dropped two cannon balls from the tower at Pisa. • Each cannon ball had a different mass • They both hit the ground at the same time • Gravity accelerates all objects at the same rate • 9.8 m/s/s (4.9m/s first second and 9.8 every second after) • .
V = 0m/s 4.9m V = 9.8m/s 14.7m or 19.6m V = 19.6m/s 24.5m or 44.1m V = 29.4m/s
V = 29.4m/s 53.9m or 98m V = 39.2m/s 93.1m or 191.1m V = 49.0m/s 142.1m or 333.2m V = 58.8m/s
V = 68.6m/s 200.9m or534.1 V = 78.4m/s 279.3m or 813.4m V = 88.2m/s 377.3m 1190.7m V = 98.0m/s 485.1m or 1675.8m V = 107.8m/s 602.7m or 2278.5m V = 117.6m/s
Gravity • Gravity accelerates all objects at the same rate • 9.8 m/s/s (4.9m/s in the first second and 9.8 every second after) • Air Resistance • Similar to friction in that it opposes the motion of a falling object in air
Gravity • Terminal Velocity • When the force of air resistance is equal to the force of gravity and a falling object no longer accelerates *
Gravity • Terminal Velocity • When the force of air resistance is equal to the force of gravity and a falling object no longer accelerates • Free fall • Only the force of gravity is pulling on an object
Gravity • Free fall . • Only the force of gravity is pulling on an object • Orbits.. • A combination of forward motion and the downward pull of gravity • Projectile Motion. • The curved path that an object takes when thrown or launched
Galileo showed us that gravity accelerates all bodies at the same rate (9.8 m/s/s) when he dropped two cannon balls from the tower at Pisa and both cannon balls hit the ground at the same time. • The astronauts of Apollo 15 verified Galileo’s observation by dropping a feather and a hammer on the moon. They too hit the ground ate the same time. • Question 1: Using you current knowledge of the laws of gravity, what would happen if you simultaneously dropped a steel ball bearing to the floor and fling a ball bearing horizontally to the ground? • Question 2: What would happen if you simultaneously dropped a bullet to the floor and shot horizontally to the ground?
Question 1: Using your current knowledge of the laws of gravity, what would happen if you simultaneously dropped a steel ball bearing to the floor and then fling a ball bearing parallel to the ground? • Question 2: What would happen if you simultaneously dropped a bullet to the floor and shot horizontally to the ground?
Gravity • Projectile Motion. • The curved path that an object takes when thrown or launched because of gravity
Question 1: Using you current knowledge of the laws of gravity, what would happen if you simultaneously dropped a steel ball bearing to the floor and fling a ball bearing horizontally to the ground? • Question 2: What would happen if you simultaneously dropped a bullet to the floor and shot horizontally to the ground?
Momentum • The product of mass and velocity • Its like inertia in motion. • P = m x v • Momentum = mass x velocity
Momentum • The momentum of an object depends on its mass and its velocity • What does that mean? • If two objects are moving at the same velocity, the object with more mass has a greater momentum. • If two moving objects have the same mass, the object with the greatest velocity has the greater momentum. • p = m · v (p = momentum)
Examples: • What is the momentum of an 8 kg ball traveling at 10m/s north? • 8 kg x 10m/s = 80 kg·m/s north
Examples: • A 1350 kg car is traveling south at 7 m/s. At the same time a 900kg car is traveling at 12 m/s. Which car has the greatest momentum? • 1350kg x 7 m/s south = 9450 kg·m/s south • 900 kg x 12 m/s south = 10800 kg·m/s south • The second car has more momentum
Conservation of Momentum • When a moving object hits another object, some or all of the momentum of the first object is transferred to the object that is hit. • What does that mean? • We have all played pool. When the cue ball strikes the object ball on the table the cue ball stops or slows down while the object ball it hits moves. • If the cue ball it struck gently the object ball move very little • If the cue ball is struck hard, the object ball moves quickly.
Conservation of Momentum • The law of conservation of momentum states that any time objects collide, the total amount of momentum stays the same.
Conservation of Momentum • Another example: • Both football players are the same weight. • If the player on the right moves at 3m/s and the player on the left moves at 2 m/s, what happens to their momentum?
Conservation of Momentum • Another example: • The player on the right weighs 200 lbs. The player on the left weight 150 lbs. • If the player on the right moves at 3m/s and the player on the left moves at 3 m/s, what happens to their momentum?
Conservation of Momentum • Another example: • The player on the right weighs 200 lbs. The player on the left weight 150 lbs. • How does the player on the left win the battle? • The player on the left has to use a greater velocity so that he can change his momentum.
In action movies we see people get shot and the impact of the bullet sends them flying backwards. Is this factual or is it Hollywood make-believe? • 150 lb man (68kg) moving 1 m/s • .45 cal bullet • Bullet weight .013 kg • Velocity 330 m/s • Man’s momentum • 68kg · 1 m/s = 68 kg · m/s • Shot momentum • .013 kg · 330 m/s = 4.3 kg · m/s • The total momentum = 63.7 kg · m/s
In action movies we see people get shot and the impact of the bullet sends them flying backwards. Is this factual or is it Hollywood make-believe? • 150 lb man (68kg) moving 1 m/s • 12 Gauge Shotgun • Shot weight .0284 kg • Velocity 397 m/s • Man’s momentum • 68kg · 1 m/s = 68 kg · m/s • Shot momentum • .0284 kg · 397 m/s = 8 kg · m/s • The total momentum = 60 kg · m/s
In action movies we see people get shot and the impact of the bullet sends them flying backwards. Is this factual or is it Hollywood make-believe? • 150 lb man (68kg) moving 1 m/s • .50 cal bullet • Shot weight .052 kg • Velocity 882 m/s • Man’s momentum • 68kg · 1 m/s = 68 kg · m/s • Shot momentum • .052 kg · 882 m/s = 46 kg · m/s • The total momentum = 22 kg · m/s
What happens if the same man is hit by a car? • 150 lb man (68kg) moving 1 m/s • car • car weight 1362kg • Velocity 10 m/s • Man’s momentum • 68kg · 1 m/s = 68 kg · m/s • Shot momentum • 1362kg · 10 m/s = 13620 kg · m/s • The total momentum = 13552 kg · m/s
Colliding pucks Air table http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=361 http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=12
