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Forces and Motion Why do objects move? A force acts on them A FORCE is a push or a pull, in any direction,that may cause a change in an object’s motion Will a force always cause an object to move? NO Every object has several forces always acting on them. Gravity Air Pressure Friction Air Pressure Friction Normal The sum of all the forces acting on an object is called NET FORCE If an object is motionless, the Net Force = 0 , The forces are said to be Balanced. With Balanced Forces, the forces are equal but in opposite directions Since the applied force is not The forces are said to be stronger than the force of friction Balanced… the object does not move Gravity Air Pressure Applied Force Air Pressure Friction Normal If a force is exerted on an object causing it to move, this is called an UNBALANCED FORCE, the net force is greater than zero and the object moves. If the applied force is strong enough than to over The applied force is stronger come the existing forces, objectofwill friction… this is an the example an move Unbalanced force Gravity Air Pressure Air Pressure Friction Applied Force Normal Some Common Forces Friction The force exerted when two objects rub up against each other. Friction opposes motion, it causes objects to slow down What affects the Friction between objects? • Mass of the Object • Type of Surface • Amount of surface area touching Sliding Friction Motion Friction Rolling Friction The amount of friction between the two objects is less than sliding friction The object is easier to move Liquid Friction A lubricant, such as oil, makes a thin layer between the two objects. Which one will move farther if an equal force is applied 200 kg 1000 kg Which one will move farther if an equal force is applied On ICE 200 kg On Carpet 200 kg Which one will move farther if an equal force is applied 200 kg 200 kg Gravity • The force that pulls objects towards each other • Every object has gravity, meaning that all objects are being pulled toward each other. • So why are we not being pulled together right now? The larger the object is, the more we are effected by its gravitational pull. We are more attracted to the Earth’s gravity than we are to gravity of the things in the room Where will the red ball move Since the green ball is bigger, its gravity effects the red ball more than the white ball does, so the red ball moves towards the green ball Why do the two objects not hit the ground at the same time? Gravity is acting more on the elephant than on the feather. And a heavier object overcomes the upward force of wind resistance (friction) more easily thus falling faster than the light object What happens if we can eliminate the wind resistance? The two objects hit the ground at the same time Gravity is still acting more on the elephant than the feather, but the inertia of the elephant keeps it from accelerating faster All objects will accelerate the same when the force of gravity is the only force action on it. Sir Isaac Newton and the 3 Laws of Motion Inertia The resistance of an object to changes in motion Basically Stated… its harder to alter the motion of a heavier object than a lighter object Newton’s First Law An object in motion will stay in motion and an object at rest will stay at rest until acted on by a force. Basically stated… objects keep moving until something slows them down (friction) and objects will stay still until something causes them to move (force) Newton’s First Law Applied: As the wall stops the car… the guy keeps going, there is nothing to stop his forward motion Newton’s First Law Applied: as the truck stops, there is nothing keeping the ladder from stopping; it continues to move forward until gravity and wind resistance stops it Newton’s Second Law Shows the relationship between an objects mass its acceleration and the applied force. Basically stated… it takes a stronger force to move a heavier object that a lighter object and a stronger force to get an object to move faster Newton’s Second Law Applied: If an equal force is applied, the less massive object moves farther 200 kg 1000 kg Newton’s 2nd Law Applied: In order to move the more massive object the same distance at, it will take a much larger force 200 kg 1000 kg Newton’s Third Law For every action, there is an opposite and equal reaction Basically stated… apply a force in one direction, there is the same force being applied right back at you Action: Thrust Reaction: Jet moves forward As the swimmer pushes against the water, the water pushes back and the swimmer moves forward Which Law Applies If you step off a boat, the boat is moved backward THIRD LAW Which Law Applies Second Law; its harder to throw a heavy object than a light one Which Law Applies? Third Law: the downward force causes the space ship to go up Which Law Applies? nd 2 law: it takes a big force to mover the heavy object First Law: The object will not move until something causes it to move Would this cart be able to make the loop on this roller coaster? Newton’s 3rd law says every action has an equal reaction… Here is the action force… Remember.. Equal… not greater… So the reaction force can only be this high… Here is the action force… The cart would only go this high then fall back