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Force Chapter 6

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Force Any push or pull exerted on an object

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System The object with the force applied

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Environment The world surrounding the object

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Contact Force A force that acts on an object by touching it

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Contact Force A baseball bat striking a ball

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Long-range Force A force that acts on an object w/o touching it

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Long-range Force The force of gravity

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Agent Whatever is causing the force

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Inertia The resistance to change (in motion)

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Equilibrium When the net forces acting on an object = zero

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Force Vector Diagram A Diagram showing the vectors of all forces acting on an object.

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Force Vector Diagram Weight on table Force of table on the ball

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Draw Force Vector Diagrams of: 1)A book on a desk 2)A book being pushed across the desk 3)A book falling

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Newton’s Laws of Motion

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Newton’s 1 st Law An object will remain at rest or in constant straight-line motion if the net force acting on it is zero

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Newton’s 1 st Law The velocity is constant and acceleration is zero when the net force on an object is zero

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Newton’s 2 nd Law The acceleration of an object is directly proportioned to the net force applied to it

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Newton’s 2 nd Law F net m a =a =a =a =

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Newton’s 2 nd Law F net = ma

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Newton’s 3 rd Law For every action, there is an equal & opposite reaction

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Newton’s 3 rd Law F A on B = -F B on A

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Two horizontal forces of 23.5 N & 16.5 N are acting in the same direction on a 2.0 kg object. Calculate: 1) net Force on the object 2) its acceleration

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Two horizontal forces of 23.5 N & 16.5 N are acting in opposite directions on a 2.0 kg object. Calculate: 1) 1) net force on the object 2) its acceleration

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Forces of 4.0 N west & 3.0 N north are acting on a 2.0 kg object. Calculate: 1) net Force on the object 2) its acceleration

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Calculate the acceleration of a 1500 g object falling towards Earth when the F air friction is 11.7 N.

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List Newton’s Laws of Motion

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Types of Forces Friction Tension Normal Thrust SpringWeight

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Friction (F f ) The contact force that acts to oppose sliding motion between surfaces Its direction is parallel & opposite the direction of sliding

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Normal (F N ) The contact force exerted by a surface on an object Its direction is perpendicular & away from the surface

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Spring (F sp ) A restoring force, or the push or pull a spring exerts on an object Its direction is opposite the displacement of an object at the end of a spring

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Tension (F T ) The pull exerted by a string, rope, or cable when attached to a body & pulled taut Its direction away from the object & parallel to the string at the point of attachment

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Thrust (F thrust ) A general term for the force that moves rockets, planes, etc Its direction is the same direction as the acceleration of the object barring any resistive forces

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Weight (F g ) Force due the gravitational attraction between two objects like an object & the Earth Its direction is straight down towards the center of the Earth

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Name & describe the 6 types of forces

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Weight (F g ) Weight = F g = ma g = mg F g = W = mg

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When an object is launched, the only forces action upon it are the forces gravity & air friction.

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No net force is required to keep an object in motion. Frictional forces oppose motion.

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Inertia is not a force, but the resistance to the change in motion or momentum.

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Air exerts huge & balanced frictional forces on an object. When in motion, the net F f of air is large.

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Terminal Velocity The constant velocity that is reached when the force of air friction of a falling object equals its weight

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Friction (F f ) Kinetic frictional force F f, kinetic Static frictional force F f, static

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Draw Vector Force Diagrams of: 1) a skydiver gaining downward velocity 2) a skydiver at terminal velocity

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Draw Vector Force Diagrams of: 3) a rope pulling a ball up at constant velocity 4) a rope acceleration a ball upwards

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An object’s weight on Earth is 490 N. Calculate: 1) its mass 2) its weight in the moon where g moon = 1.60 m/s 2

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An 500.0 g object on an unknown planet has a weight of 250 N. Calculate the acceleration caused by the planet’s gravity.

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Static F f The force exerted on one surface by another when there is no relative motion

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Kinetic F f The force exerted on one surface by another when in relative motion

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Forces acting on an object: F N = -W F A > F f F applied F g or Weight FfFfFfFf FNFNFNFN

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Static F f F f, static = s F N

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s is proportionality constant called the frictional coefficient

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Kinetic F f F f, kinetic = k F N

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A 25 N force is required to pull a 50.0 N sled down the road at a constant speed. Calculate the sliding frictional coefficient between the sled & the road.

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A person & a sled have a total weight of 490 N. The sliding frictional coefficient between the sled & the snow is 0.10. Calculate the force required to pull the sled at constant speed.

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Calculate the acceleration of the sled if the applied force pulling on the sled is 299 N. W = 490 N = 0.10

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Calculate the force required to pull a 500.0 g block with an acceleration of 3.0 m/s 2. = 0.50

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Periodic Motion Repetitive or vibrational motion like that of a spring, swing or pendulum

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Simple Harmonic Motion Periodic motion in which the restoring force is directly proportional to the displacement

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Period (T) The time required to complete one full cycle of motion

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Amplitude Maximum displacement from the zero point or equilibrium

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Pendulum Motion Formula T = 2 ---- l agagagag

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Calculate the period of a pendulum with a length of 49 cm:

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Calculate the length of the pendulum of a grandfather clock whose period is equal 1.0 second:

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Fundamental Forces Gravitational Electromagnetic Strong Nuclear Weak Nuclear

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Calculate the force required to pull a 150 g block at a constant velocity of 180 km/hr. = 0.20

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A 9.8 kN car went from 0 to 25 m/s in 5.0 s. between car & road = 0.20. Calculate the force applied by the engine of the car.

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Calculate the force required to start a 2.0 kg block & its acceleration when moving. s = 0.20, k = 0.10

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Calculate the force required to start a 2.0 kg block & calculate its acceleration when moving. s = 0.20, k = 0.10

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A 6.0 kg ball is attached by a rope over a pulley to a 4.0 kg ball. 1) 1) Draw the problem. 2) 2) Calculate each ball’s acceleration

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A 6.0 kg ball is attached by a longrope over a pulley to a 4.0 kg ball. 1) 1) Calculate air friction at max velocity

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A 65 kg boy & a 35 kg girl are in a tug-of-war. The girl’s acceleration is 13 cm/s 2. Calculate the boy’s acceleration.

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A 150 g baseball, was hit & came to rest in 4.0 s after going 100.0 m. Calculate: v i, a, & F f on the ball.

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A 50.0 kg box falls off a 0.49 km cliff. 1) 1) Calculate v i, v f, a, & t. 2) 2) Calculate F f if air friction is included

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A 10.0 kg box falls off a 0.49 km cliff & hits the ground in 20.0 s. 1) 1) Calculate v f & a. 2) 2) Calculate F f if air friction is included

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Calculate the force required to pull a 250 g block at a constant velocity of 360 km/hr. = 0.30

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Calculate the force required to accelerate a 1500 g block along the floor at 3.0 m/s 2. = 0.25

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Calculate the apparent weight of a 50.0 kg person on a scale on an elevator descending at 2.0 m/s 2.

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Calculate the apparent weight of a 50.0 kg person on a scale on an elevator ascending at 2.0 m/s 2.

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Calculate the period of the pendulum on Big Ben which is 4.9 m long.

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Calculate the force required to accelerate a 10.0 kg block straight up at 25 cm/s 2.

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Calculate the force required to accelerate a 50.0 kg block straight up over a pulley at 5.0 m/s 2.

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Calculate the acceleration of a system of a 55.0 kg block tied to a 45.0 kg block hanging over a pulley.

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Calculate the frictional coefficient of a 100.0 kg block if a 150 N force causes it to accelerate at 50.0 cm/s 2.

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Calculate the frictional coefficient of a 10.0 kg block if a 98 N force causes it to slide at 30.0 cm/s.

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A 5.0 N force accelerates a 1000.0 g block at 45.0 cm/s 2. Calculate K.

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Calculate the acceleration of a system of a 200.0 kg cart on a plane tied to a 50.0 kg block hanging over a pulley.

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