Transcript Force
What is a Force? FORCE = Any push or pull which causes something to move or change its speed or direction What is a Force? Forces can be BALANCED or UNBALANCED Balanced forces are equal in size and opposite in direction Unbalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results. Amusement Park Forces What is a Force? Can you think of examples of forces? Balanced Forces? Unbalanced Forces? What is Gravity? GRAVITY: An attraction force between all masses Newton’s universal law of gravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe The amount of gravitational force depends upon the mass of the objects and the distance between the objects What is Gravity? The greater the mass, the greater the force of gravity. The greater the distance, the lesser the force of gravity Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2 Gravity in Space Weight is a measure of the gravitational force between two objects The greater the mass the greater the force (weight) Force measured in units called Newtons (N) Weightlessness – a feeling of freedom from the effects of gravity. Gravity by Brainpop 1) How does the gravity on the moon compare to the gravity on Earth? Why? 2) Why don’t you notice your own gravitational pull on the Earth? 3) On what two things does the force of gravity depend? Roller Coaster Physics I. HANG ON!l Air resistance: The force of air exerted on a falling object The air pushes up as gravity pulls down Dependent upon the shape and surface area of the object When the air resistance equals the force of gravity, terminal velocity is reached Terminal velocity is the highest velocity that an object will reach as it falls Look out below! How is this possible? I. The Science Geeks What is Friction? Friction = A force that opposes or slows down motion Caused by the physical contact between moving surfaces The amount of friction depends upon the kinds of surfaces and the force pressing the surfaces together Changes motion into heat 3 Types of Friction I. Static Friction: Friction that acts on something that is not moving I. Piano is held in place by static friction II. Static friction keeps you in your seat III. No heat or wear is generated Friction # 2 I. Sliding Friction: Force resulting when pushing or pulling an object over a surface. I. II. Moving day—pushing a box across the floor Heat and wear can result Friction # 3 I. Rolling Friction: Contact is reduced because of rollers or wheels or ball bearings. I. Skate boards have ball bearings in the wheels. II. A cart has wheels. III. Less heat and wear will result. What are some ways athletes uses friction? First Law: An object at rest stays at rest or an object in motion, stays in motion (in the same direction/at the same speed) unless acted upon by an unbalanced force Also called the law of inertia Inertia A property of matter The tendency of an object to resist any change in its motion The greater the mass the greater the inertia The greater the speed the greater the inertia Examples of Newton’s 1st Law a) car suddenly stops and you strain against the seat belt b) when riding a horse, the horse suddenly stops and you fly over its head c) the magician pulls the tablecloth out from under a table full of dishes d) the difficulty of pushing a dead car e) Playing soccer on a cut and rolled lawn verses an uncut lawn f) car turns left and you appear to slide to the right Examples of Newton’s 1st Law Second law: The greater the force applied to an object, the more the object will accelerate. It takes more force to accelerate an object with a lot of mass than to accelerate something with very little mass. The player in black had more acceleration thus he hit with a greater amount of force Second law: The greater the force, the greater the acceleration The greater the mass, the greater the force needed for the same acceleration Calculated by: F = ma (F = force, m = mass, a = acceleration) Examples of Newton’s 2nd Law a) hitting a baseball, the harder the hit, the faster the ball goes b) accelerating or decelerating a car c) The positioning of football players - massive players on the line with lighter (faster to accelerate) players in the backfield d) a loaded versus an unloaded truck Examples of Newton’s 2nd Law The second law states that unbalanced forces cause objects to accelerate with an acceleration which is directly proportional to the net force and inversely proportional to the mass. This one is telling us that big heavy objects don’t move as fast or as easily as smaller lighter objects. It takes more to slow down a charging bull then to slow down a charging mouse. third law: For every action force, there is an equal and opposite reaction force. (Forces are always paired) Examples of Newton’s 3rd Law a) rockets leaving earth b) guns being fired c) two cars hit head on d) astronauts in space e) pool or billiards f) jumping out of a boat onto the dock g) sprinklers rotating rd Examples of Newton’s 3 Law Newton’s third law: "For every action, there is an equal and opposite reaction." When you fire a gun you feel the recoil. Some of the funniest things in cartoons follow physics that have been exaggerated or just plain ignored. Wyle E. Coyote hangs suspended in space over that canyon for a lot longer than an object would in reality, but it is the anticipation of the drop and Wyle's facial recognition of the upcoming pain that is so classically cartooney. So some laws are stretched for comical effect. Examples of Newton’s 3rd Law Momentum: The quantity of motion A property of moving objects Calculated by: P = mv (p = momentum, m = mass, v = velocity) Law of conservation of momentum: the total amount of momentum of a group of objects does not change unless outside forces act on the objects Rollercoaster Momentum Newton’s Laws by Brainpop 1) Why does a ball roll across a rug and come to a stop? 2) What is a net force? 3) Give an example of Newton’s 3rd Law: Force by Brainpop 1) What famous physicist are units of force named after? 2) What does velocity measure? 3) If Moby has a mass of 50 kg and Tim has a mass of 40 kg, who would require more force to move?