Transcript Force
MOTION AND FORCES Motion - a change in position of an object, caused by an object Force – a push or a pull, caused by another object Force Can – Start Motion Stop Motion Change its direction KINDS OF FORCE TAKE NOTES! There are many different kinds of force. There are pushes and pulls electromagnetic forces weak forces strong forces and gravitational forces, Some forces are referred to as contact forces and some are non-contact forces TAKE NOTES! FORCES RELATED TO BASIC PROCESSES Blood flow in the body Plate movement (tectonics) Volcanic eruptions Earthquakes Mountain building Emergence of seedlings Erosion A NET FORCE RESULTS IN A CHANGE OF MOTION The net force is the “left over” amount when all the forces are added (no net force) If there is a net force, the object will change its direction or velocity. This is called acceleration Newton’s First Law of Motion – Law of Inertia (Was really discovered by Galileo in 1600) An object will remain at rest or move in a straight line unless it is acted on by a force. Force - a push or a pull = Newton (N) 1 Newton = 1 kg x m/s2 Gives ENERGY to an object Contact force - involves objects touching each other Long range forces - include gravity, magnetism, & electricity Inertia - measures an object’s tendency to remain at rest or keep moving - it is related to mass TAKE NOTES! Balanced forces - when the forces are equal but in opposite directions, they will cancel each other out. Does not cause motion. Unbalanced forces - uneven forces acting on an object that did not cancel each other out. The object will move in the direction of the larger one. Cause motion. Friction - is a force that resists motion between surfaces that are touching. Static Friction - hinders a stationary object from moving on a surface when a force is applied to the object. Sliding Friction- occurs when two surfaces slides past each other Rolling Friction - is the force that enables a wheel to roll past on a surface-same direction Air Resistance - molecules in air colliding with the forward-moving surface of an object, slowing its motion. Newton’s Second Law of Motion An object acted on by an unbalanced force will accelerate in the direction of the force, according to the formula. Acceleration = Force (Newton) (10N) = 5N/kg or 5m/s2 Mass (Kilogram) (2kg) Force of Gravity = Force= m x (9.8 m/s2) 9.8m/s2 = acceleration Mass vs. Weight - Mass is the measure of the amount of matter in an object it remains the same. Weight is a force = mass x (9.8 m/s2) gravity (Mass is a measure of inertia.) If a 50 kg person in the middle of an ice skating rink pushes a 20 kg box with a force of 10 N, what will the acceleration be? 50 Kg person 10 N Force 20 Kg box Acceleration of the box: Acceleration = force mass a = (10 N) (20 Kg) a = .5m/s2 Acceleration of the person: Acceleration = force mass a = (10 N) (50 Kg) a = .2m/s2 TAKE NOTES! WEIGHT IS A TYPE OF FORCE Mass is a measure of how much matter an object contains. Weight is the result of the force of gravity pulling on a mass. The greater the force of gravity, the greater the weight. Newton’s Third Law of Motion For every action, TAKE NOTES! there is an equal, but opposite reaction. Force always acts in equal and opposite pairs. (Not the same as balanced forces - different objects.) When you walk, you push backward on the ground, and the ground pushes forward on you. If you put two bar magnets with opposite poles facing one another, they will move toward each other. TAKE NOTES! Gravity is a force of attraction between objects. The amount of the force depends on the mass of each object and the distance between them. GRAVITY IS A NON-CONTACT FORCE The earth pulls on the moon while the moon also pulls on the earth. The sun pulls on the earth and moon (and other planets) and the earth and moon pull on the sun The earth pulls on other planets and they also pull on the earth Gravity and the third law Gravity is pulling you to earth and Earth is also pulled toward you. The same force that keep planets in orbit, is the same force that pulls objects down to Earth. You apply a force to earth, but because earth is more massive than you are, your force has little or no effect. (While F is greater, so is m the mass.) Newton’s laws apply to all objects, including distant galaxies. Just as the Sun exerts a gravitational force on Earth, Earth exerts an Equal and opposite force on the Sun. This causes a variation in the Sun’s rotation. Combining the Laws 2. You leave the ground, you accelerate in the direction of this unbalanced force 2nd law accelerate in direction of the unbalanced force. 3. When your feet hit the ground, the ground exerts an upward force on you. When you stop accelerating, all of the forces are balanced. 1st law you remain at rest. 1. You push on the ground, it pushes up on you. 3rd law - equal/opposite reaction Combining the Laws 1st Law - The canoe will stay until a force moves it. This force comes from the push of the puddles. 2nd Law - The canoe changes speed or direction or both. The people add mass and the paddlers change the canoe’s acceleration by adding a lot of force 3rd Law - The paddlers push water backward an action. This backward force produces an equal and opposite forcea reaction in the water - that move the canoe forward.