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Force. Chapter 6. Force. Any push or pull exerted on an object. System. The object with the force applied. Environment. The world surrounding the object. Contact Force. A force that acts on an object by touching it. Contact Force. A baseball bat striking a ball. Long-range Force.
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Force Chapter 6
Force • Any push or pull exerted on an object
System • The object with the force applied
Environment • The world surrounding the object
Contact Force • A force that acts on an object by touching it
Contact Force • A baseball bat striking a ball
Long-range Force • A force that acts on an object w/o touching it
Long-range Force • The force of gravity
Agent • Whatever is causing the force
Inertia • The resistance to change • (in motion)
Equilibrium • When the net forces acting on an object = zero
Force Vector Diagram • A Diagram showing the vectors of all forces acting on an object.
Force Vector Diagram Force of table on the ball Weight on table
Draw Force Vector Diagrams of: • A book on a desk • A book being pushed across the desk • A book falling
Newton’s 1st Law An object will remain at rest or in constant straight-line motion if the net force acting on it is zero
Newton’s 1st Law The velocity is constant and acceleration is zero when the net force on an object is zero
Newton’s 2nd Law The acceleration of an object is directly proportioned to the net force applied to it
Newton’s 2nd Law Fnet m a =
Newton’s 2nd Law Fnet = ma
Newton’s 3rd Law For every action, there is an equal & opposite reaction
Newton’s 3rd Law FA on B = -FB on A
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 object2) its acceleration
Two horizontal forces of 23.5 N & 16.5 N are acting in opposite directions on a • 2.0 kg object. Calculate: • net force on the object • 2) its acceleration
Forces of 4.0 N west & 3.0 N north are acting on a 2.0 kg object. Calculate: 1) net Force on the object2) its acceleration
Calculate the acceleration of a 1500 g object falling towards Earth when the Fair friction is 11.7 N.
Types of Forces Friction Tension Normal Thrust Spring Weight
Friction (Ff) • The contact force that acts to oppose sliding motion between surfaces • Its direction is parallel & opposite the direction of sliding
Normal (FN) • The contact force exerted by a surface on an object • Its direction is perpendicular & away from the surface
Spring (Fsp) • 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
Tension (FT) • 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
Thrust (Fthrust) • 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
Weight (Fg) • Force due the gravitational attraction between two objects like an object & the Earth • Its direction is straight down towards the center of the Earth
Weight (Fg) Weight = Fg = mag = mg Fg = W = mg
When an object is launched, the only forces action upon it are the forces gravity & air friction.
No net force is required to keep an object in motion. Frictional forces oppose motion.
Inertia is not a force, but the resistance to the change in motion or momentum.
Air exerts huge & balanced frictional forces on an object. When in motion, the net Ff of air is large.
Terminal Velocity • The constant velocity that is reached when the force of air friction of a falling object equals its weight
Friction (Ff) Kinetic frictional force Ff, kinetic Static frictional force Ff, static
Draw Vector Force Diagrams of: 1) a skydiver gaining downward velocity 2) a skydiver at terminal velocity
Draw Vector Force Diagrams of: 3) a rope pulling a ball up at constant velocity 4) a rope acceleration a ball upwards
An object’s weight on Earth is 490 N. Calculate:1) its mass2) its weight in the moon where gmoon = 1.60 m/s2
An 500.0 g object on an unknown planet has a weight of 250 N. Calculate the acceleration caused by the planet’s gravity.
Static Ff • The force exerted on one surface by another when there is no relative motion
Kinetic Ff • The force exerted on one surface by another when in relative motion
Forces acting on an object: FN FN = -W FA > Ff Ff Fapplied Fg or Weight
Static Ff Ff, static = msFN