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Understand the concept of force and its effects on objects through visuals and explanations. Learn about contact and action-at-a-distance forces, balanced and unbalanced forces, and various types of forces in different scenarios.
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Warm Up – 11/29/16 • How would you define the term force? What does a force do?
Forces Foldable: title each flap and draw a picture, then include all information listed below
The Nature of Force • A force gives energy to an object, sometimes causing it to start moving, stop moving, or change direction. • A force can be a push or pull. • Newton: the unit used to express force (I pushed the chair with 50 N of force) • Net Force: the combination of all forces acting on an object
Contact forces are types of forces in which the two interacting objects are physically contacting each other. Applied Force Frictional Force Tensional Force Normal Force Air Resistance Force (which is a type of frictional force) Spring Force Action-at-a-distance forces are types of forces in which the two interacting objects are not in physical contact witheach other, yet are able to exert a push or pull despite a physical separation. Gravitational Force Electrical Force Magnetic Force Centripetal Force Types of Forces
Forces Acting in the Same Direction • When multiple forces act upon an object in the same direction, you ADD the forces to find the net force acting on the object.
Forces Acting in Opposite Directions • When multiple forces act upon an object in the opposite directions, you SUBTRACT the forces to find the net force acting on the object.
Balanced Forces • Balanced forces cause NO CHANGE in motion • Forces that are in opposite directions and equal in size are called balanced forces. • When forces are balanced, there is no change in motion; there would be no overall force (net force) acting on the object.
Unbalanced Forces • Unbalanced forces cause a CHANGE in motion Same direction • When two forces are acting in thesame direction, they are added together. • The size of the arrow is relative to the strength of the force. • This force is unbalanced because there is a change in motion
Unbalanced ForcesSame Direction • They each provide an “applied force” in the same direction. Meanwhile, gravitational force and frictional forces are working against them. • Since Frank and John’s combined forces are greater, then the piano moves! • The net force is “unbalanced” Frank and John are pushing the piano on its wheels to move it.
Unbalanced Forces-Opposite directions • When two forces act in opposite directions, they combine by subtraction, • If one force is greater than the other force, the object will move in the direction of the greater force (tug-of-war). This force is unbalanced because there is a change in motion
Unbalanced Forces • In this game of tug of war, the red dog is losing ground. • The applied force of the red dog is not as great as the applied force of the gray dog. • Net force is unbalanced, and in the direction of the gray dog.
Tensional Force –when things are pulling in opposite direction
Recognizing Forces Choose from these forces • Applied Force • Frictional Force • Tensional Force • Normal Force • Air Resistance Force • Spring Force • Gravitational Force • A skydiver (who hasn't opened his parachute yet) falls at terminal velocity. Consider the forces acting on the skydiver. • A block rests on top of a table. Consider only the forces acting upon the block. • A block slides across the top of a table. Consider only the forces acting upon the block.
Recognizing Forces Choose from these forces • Applied Force • Frictional Force • Tensional Force • Normal Force • Air Resistance Force • Spring Force • Gravitational Force • A block hangs at rest from the ceiling by a piece of rope. Consider the forces acting on the block. • A ball is shot into the air with a spring-loaded cannon. Consider the forces acting on the ball while it is in the air. • The wheels of a car are locked as it skids to a stop while moving across a level highway. • A car is attached by a cable to a moving truck and is being pulled along a level highway. Consider only the forces acting on the car.
Force Diagrams Applied Force Force of Gravity Normal Force Force of Friction
Label the forces involved in Tom Brady’s winning Touchdown throw!
Friction • Friction is all around us. Caused by the minor bumps and jagged edges in all surfaces there is no way for humans to escape it! One source even called it “the ‘evil’ of all motion” (Jackson). There are 4 types of friction: static, sliding, rolling and fluid. Each of these have their own unique application and advantages. There are pro’s and cons to friction as well as ways to decrease friction. Understanding these things will help us use friction to our advantage as well as lessen it when it becomes a frustration in daily life.
Warm Up • In your own words, write a definition of the word friction. What is one way that friction can be increased?
Friction: A Force Opposing Motion • Friction is a force that acts in a direction opposite to the motion of the moving object causing the moving object to slow down and finally stop. • Friction arises from the fact that objects and surfaces are not perfectly smooth. • The amount of friction between two surfaces depends on how hard the surfaces are forced together and on the materials of which the surfaces are made.
Slidingfriction • When solid objects slide over each other, they produce slidingfriction. In order to move the object you must exert a force larger than the force of friction. • The amount of sliding friction depends on: • weight of the moving object. • type of surface that the object is sliding across.
Rollingfriction When an object rolls over a surface rolling friction is produced Produced by objects such as wheels and ball bearings it tends to be less than that of sliding friction.
Fluid friction As an object moves through a fluid it produces fluid friction fluid friction is less than sliding friction. Air resistance is an example of fluid friction caused by the particles that make up air. All liquids and gases are fluids Friction also exists when an object moves across or through a fluid. Substance called lubricants (oil, wax, and grease), change sliding friction to fluid friction, thus reducing friction.
Static Friction • When a force is applied to an object but does not cause it to move. • The force of static friction balances the applied force. • Static friction disappears as soon as an object begins to move.
Friction: Is it helpful or harmful? • An example: • In your car friction can be both helpful and harmful, here is how: • When you press on the breaks you cause friction between them which HELPS slow down your car • In this same car there is friction between the moving parts in the engine. This friction causes the parts to wear out over time and therefore they must be replaced. • Friction between your foot and shoe can make holes in your socks! • Friction between your shoe and the floor helps you to stand upright.
Warm Up • Give an example of how friction can be harmful when running a car. Then give and example of how it could be helpful. Try to identify the type of friction involved in your example.
Friction Assignment: • You will create a poster advertising a type of friction. What your poster must include: • An illustration with the direction of forces and motion labeled. Make sure the size of your arrows match the size of the force. • Include in you poster the definition of friction and the definition of your chosen type of friction. • Include a statement explaining how friction is playing a roll in your illustration. • Be neat, creative and add some color to your poster!
Friction is not always a problem . . . as a matter of fact, in many cases it can be helpful. • How might we lessen the amount of slide friction?
Warm Up • Significantly decreased gravity gives astronauts the sensation of being weightless and forces astronauts to make many adjustments in their activities. Write a paragraph explaining what you would like and dislike about living with reduced gravity.
Why does an apple fall towards the ground when dropped? • Isaac Newton asked this question in 1665. • The answer to this question gave birth to a law…
The Law of Universal Gravitation • All objects in the universe attract each other through gravitational force. • The size of this force depends on the masses of the objects and the distance between them. • So… • Gravitational force increases as mass increases. • Gravitational force decreases as distance increases.
On Earth, all objects experience a "downward" force of gravity. • The force of gravity on an object is always equal to the weight of the object. • Gravity is of great importance in the interaction of all objects in the universe; • it binds us to the Earth, • holds the Earth and all planets in the solar system, Gravity is what holds the universe together
Weight • Your weight varies according to the force of • gravity pulling on you • The force of gravity varies according to the • distance the object is from the center of the Earth. • - You weigh less on top of a mountain than you do at sea level. Weight is • a measure of the force of gravity on an object • Metric or SI unit is the Newton (N)
Calculate your weight • Weight (N) = Mass (kg) x 9.8 • Your mass (kg) can be found in two ways…. • Mass = your pounds ÷ 2.2 • There are 2.2 lbs in 1 kg • Mass = your pounds x 0.4545 • There is about 0.4545 kg in 1 pound
Ball Drop Investigation • You have been given two balls, predict which ball will hit the ground first if dropped from the same height. • Now, with your neighbor, try it! • Were the results what you expected? Why or why not? • Now, predict what would happen is you dropped a piece of paper and the golf ball. • Now try it! – what happened? Were the results what you expected? Why or why not? • How could you get the paper to drop at the same rate as the golf ball?
Gravity in Motion • All objects fall to the ground at the same RATE because the acceleration due to gravity is the same for all objects. • This is because heavier objects experience more gravitational pull but are also harder to accelerate than a lighter object.
Acceleration Due to Gravity • ALL objects accelerate toward earth at a rate of 9.8 m/s/s. • How do we calculate an objects change in velocity during free fall? • Change in velocity= g x t • g=acceleration due to gravity • t=time
Warm Up 11/27 • A girl goes to the doctor and finds that she weighs 95 pounds. What is her weight in Newtons? • M = lb / 2.2 • M = 95/2.2 • M = 43.18 kg • W = kg*9.8 • W = 43.18*9.8 • W = 423.16 N