2Newton’s 2nd law2nd – an object accelerates in the direction of the net force acting upon itA= net force/Massa= Fnet/mA force on an object is equal to the change in momentum of the objectForce = mass * accel.F=m*a
3PracticeYour push your friends trike with a force of 150N, his mass is 35kg the trikes is 15kg, what is the acceleration?150N/50kg=3m/s/s
4FrictionFriction is the force that opposes motion between two opposing surfacesFriction always acts against motionCauses of friction – unsmooth surface, deformations, molecular attraction
52 types of friction Static friction – force of a resting object Static friction – force of a resting objectSliding or Kinetic friction - force on a moving objectMicrowelds- deformations that hold cause static frictionEver notice how it takes more force to get an object moving
6Air resistanceWhen drag is equal to weight, there is no net external force on the object.The object then falls at a constant velocity as described by Newton's first law of motion.The constant velocity is called the terminal velocity.This is due to the air resistance – Friction force caused when objects fall through airDependant upon the speed, shape, mass, and size of the object, and the density of the air.
7More massive objects fall faster than less massive objects because they are acted upon by a larger force of gravity; for this reason, they accelerate to higher speeds until the air resistance force equals the gravity force.
8Stuff falls http://www.youtube.com/watch?v=5C5_dOEyAfk All objects near the surface of the earth accelerate at a rate of 9.8m/s/sObjects of different masses will fall at the same rate regardless of their mass
9Where is he falling fastest. Where is accelerating the most Where is he falling fastest? Where is accelerating the most? Where is he not accelerating?
10Gravitational accelertion More force acts upon a more massive object, but its larger mass requires more force to accelerate.There is a myth about Galileo dropping canon balls off the leaning tower of Pisa to prove this.
12Gravitational acceleration Velocity of a freefalling object can be found with the formula v= g*tWhere gravities acceleration is 9.8m/s/sHow can you find falling distanceD= ½ g *t2
13CentripetalCentripetal acceleration: acceleration toward the center of a curved pathCentripetal means center seeking- it is merely a net force
14Centripetal ex.forceAs a bucket of water is tied to a string and spun in a circle, the force of tension acting upon the bucket provides the centripetal force required for circular motionAs a car makes a turn, the force of friction acting upon the turned wheels of the car provide the centripetal force required for circular motion.As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion – p.s. the moon is a banana
15Weight Weight – The measure of the force of gravity on a body. On earth your weight in Newtons (N) is equal to your mass in kg times gravity’s acceleration (9.8m/s2)W= m * g
16WeightlessnessWeightlessness is sensation experienced when there are no external objects touching one's body and exerting a push or pull
17Astronauts on the orbiting space shuttle are weightless because.. a. there is no gravity in space and they do not weigh anything.b. space is a vacuum and there is no gravity in a vacuum.c. space is a vacuum and there is no air resistance in a vacuum.d. the astronauts are far from earth's surface at a location where gravitation has a minimal effect.
18Freefallin’Orbit is a state of constant freefall – the Earth’s surface is falling away at the same rate of orbit400 km above the earth's surface, the the value of g will have been reduced from 9.8 m/s/s (at earth's surface) to approximately 8.7 m/s/s. About 10% less than the surface
19Projectile motionProjectile motion: Anything that has horizontal motion is a projectileHorizontal and vertical motion act independently of one another-Projectiles follow a path called a trajectory
29PracticeA scooter and a big red truck, both moving at 20m/s. Which has more momentum.Mass of red truck 3000kgMass of scooter 8kgMomentum of truck:of Scooter:
30Force and momentumObjects with momentum can apply force to other objects when they strike each otherF=mvf – mvi/tThis is a formula combining the 2nd and 3rd lawsA baseball strikes your glove with a velocity of 49m/s, its mass is .145kg. The ball comes to a stop in .05s. What force is applied?
31Artificial Satellite vs. Natural Satellite Sputnik: 1957 Russian (October 4th) “Fellow Traveler or Satellite”What do we use satellites for?Weather TV Communications Science and Research
32Satellites How many satellites currently orbit the earth? Geosynchronous Satellites: Orbital speed matches the earth’s rotationWhere? 35,790 km above the equator.International Space Station: 390 km