Physics I Honors 1 Happy New Quarter day I sent an arrow into the air and it landed I know not where. But, It was launched at 30 degrees with a velocity of 50m/s. So, how long was it airborne???

Physics I Honors 2 (1)Dynamics Newton’s Laws

Physics I Honors 3 Dynamics Dynamics is the study of forces and the resulting motion. Here, we study acceleration and its cause…force Force the agency of change. changes the velocity. is a vector quantity. measured in Newton’s.

Physics I Honors 4 Newton’s First Law: The Law of Inertia Inertia is the tendency of a body in motion to stay in motion and a body at rest to stay at rest.

Physics I Honors 5 What is Inertia? Inertia is the property of matter to resist change in motion Mass is the measure of inertia Mass is measured in kilograms (kg) How and when will mass change???

Physics I Honors 6 Newton’s First Law When an object is at rest or at constant velocity, its acceleration is zero. Under these conditions the object is said to be in a state of equilibrium. An object in the state of equilibrium has no net forces acting upon it. A net force (unbalanced force) is needed to change the state of motion of an object.

Physics I Honors 7 Newton’s Second Law: Newton’s Second Law: The Law of Acceleration A net force causes an acceleration. Force is directly proportional to acceleration. F  a The resulting acceleration is inversely proportional to the mass of the object a  1/m F = ma is the single most important equation in Physics.

Physics I Honors 8 Newton’s Second Law The Newton (N) is the unit of force. 1 N = kg·m/s 2 A 1.00 kg mass that undergoes a 1.00 m/s 2 acceleration is experiencing a force of 1.00 Newton.

Physics I Honors 9 Twice as much force produces twice as much acceleration Twice the force on twice the mass gives the same acceleration Force of hand accelerates the brick The same force accelerates 2 bricks 1/2 as much 3 bricks, 1/3 as much acceleration

Physics I Honors 10 Newton’s Third Law: The Law of Action and Reaction Forces For every force on an object, there is always an equal and opposite force exerted by the object. Forces always come in pairs known as action- reaction pairs. Action: tire pushes on road Reaction: road pushes on tire Action: gas pushes on rocket Reaction: rocket pushes on gas

Physics I Honors 11 Action-Reaction Pairs Action: man pulls on spring Reaction: spring pulls on man Action: Earth pulls on ball Reaction: ball pulls on Earth In the interaction between the hammer and the stake, each exerts the same amount of force on the other.

Physics I Honors 12 Even objects at rest on a surface have pairs of forces acting on them.

Physics I Honors 13 The force exerted against the recoiling rifle is just as great as the force that drives the bullet. Why, then, does the bullet accelerate more than the rifle?

Physics I Honors 14 (2)Dynamics Weight vs Mass

Physics I Honors 15 Mass vs Weight Mass is –the quantity of matter in an object…the amount of stuff…measured in kilograms. –is the measure of the inertia of an object. Weight (F W ) is –the measure of the gravitational force on an object. –a force F w = mg –is measured in Newtons (N).

Physics I Honors 16 Mass vs Weight An anvil in outer space, between the Earth and Moon, for example, may be weightless, but it is not massless. The astronaut in space finds it is just as difficult to shake the "weightless" anvil as it would be on Earth.

Physics I Honors 17 Two Kinds of Mass Gravitational Mass – the mass measured by a beam balance or spring scale – measured from gravity. Inertial Mass – the mass of an object is the ratio of the net force exerted on the object and its acceleration.

Physics I Honors 18 The ratio of weight (F w ) to mass (m) is the same for all objects in the same locality; hence, their accelerations are the same in the absence of air resistance.

Physics I Honors 19 (3)Dynamics Free Body Diagrams Net Forces Equilibrium

Physics I Honors 20 Forces Come in Many Forms All forces can be calculated using F = ma Be sure to identify your forces. –Net ForceF Net –Normal ForceF N –Applied ForceF A –Opposing ForceF o –Frictional ForceF f –TensionF T –Lift ForceF L –Drag ForceF D

Physics I Honors 21 Free Body Diagrams Display all of the forces on an object at a given time. Use an abstract form (rectangle, circle, etc.) to represent the object. Are indicated by arrow pointing in the direction of the force. The length of the arrow is relative to the magnitude of the force.

Physics I Honors 22 FBD of an object moving across a flat surface

Physics I Honors 23 Net Force The net force is the sum of all forces acting on an object. –When two forces act on an object the forces are cumulative (they are added together). –Net force is called a resultant and can be calculated using geometry.

Physics I Honors 24 Net Force The net force is the sum of all the forces acting on an object in a given direction.

Physics I Honors 25 Net Force The rate and the direction of movement of this ship are determined by a combination of direction and magnitude of force from each of the tugboats. Which direction are the two tugboats pushing? If the tugboat by the numbers is pushing with a greater force and the back tugboat is keeping the ship from moving, what will happen?

Physics I Honors 26 Forces are Vectors so Directions are Important Force #1 Force #2 Force #1 Force #2 Total Force Total Force = 0

Physics I Honors 27 (A)When two parallel forces are acting on the cart in the same direction, the net force is the two forces added together. 10 N east 20 N east

Physics I Honors 28 (B) When two forces are opposite and of equal magnitude, the net force is zero. 10 N west 10 N east0 N

Physics I Honors 29 (C) When two parallel forces are not of equal magnitude, the net force is the difference in the direction of the larger force. 20 N west 10 N east10 N west

Physics I Honors 30 Net Force Force on person by box Force on floor by box Force on box by floor It’s the sum of all the forces that determines the acceleration Force on box by person

Physics I Honors 31 Equilibrium If the net forces on an object equal zero, the object is in equilibrium. Net force of zero means no acceleration. It may be at rest Or, it may be moving at a constant velocity.

Physics I Honors 32 Forces in a Single Plane Horizontal Force applied opposes the force of friction. F NET = F a + F f Vertical Force applied opposes the force of gravity, that is, the weight. F NET = F a + F f

Physics I Honors 33 Normal Force The normal force (F N ) on an object supported by a surface is the component of the supporting force that is perpendicular to the surface. When an object is sitting on a level surface then the normal force is always equal and opposite of the weight of the object

Physics I Honors 34 Normal Force Anytime two surfaces are in contact there will be a normal force Normal force is always perpendicular to the surfaces so; The word Normal is often synonymous with the word perpendicular!

Physics I Honors 35 (4)Dynamics Friction

Physics I Honors Happy Hallow’s Eve A lighter than air balloon is accelerating upwards at 2m/s/s. Its total mass is 2000 kg. What must be the net force? Bonus: What is the lift force? 36

Physics I Honors 37 Friction Is the force that opposes the motion of two surfaces in contact. Static Friction friction that opposes the start of motion friction from rest. Sliding Friction friction of motion friction from constant velocity. Static frictional forces always greater than sliding ones

Physics I Honors 38 The force of friction depends on two things… The nature of the surfaces in contact…the coefficient of friction. The force pushing the surfaces together…the normal force. F f =  F N

Physics I Honors 39 What’s Happening With Friction F a > F f  acceleration F a < F f  deceleration F a = F f  equilibrium

Physics I Honors 40 (4)Dynamics Forces on an Inclined Plane

Physics I Honors 41 What is an Inclined Plane? An inclined plane is a simple machine designed to –Reduce the amount of force required to do a given quantity of work –By extending the distance over which the force is exerted.

Physics I Honors 42 Components