Force Open Stax College Newtons Laws Ancient scientists

Force Open. Stax. College

Newton’s Laws ] Ancient scientists looked to the natural properties of objects. • Motion was a result of the object’s properties. ] Newton defined motion based on forces acting from outside an object. • Motion was the result of external forces. ] Three laws were used to define the behavior of forces on objects.

Fundamental Forces ] ] Gravity is a fundamental force. It acts upon objects from a distance away from the source (such as the Earth). There are two other fundamental forces. Electroweak force is common in everyday life. • • Electricity Magnetism Light Radioactive decay ] Nuclear force is uncommon in everyday life. • Nuclear fission (nuclear power plants) • Nuclear fusion (stars)

Contact Forces ] Many forces are due to contact between objects. • • ] Kick a ball Push with a bulldozer Tug from a rope Friction due to the ground The actual force is electricity, but the atoms are so small we can treat the forces as coming from contact by larger objects.

First Law: Law of Inertia 1 An object continues at rest, or in uniform motion in a straight line, unless a force is imposed on it. ] ] This describes constant velocity, including zero. No change means no force, and vice versa. no force rocket constant velocity

Zero Net Force ] An object at rest with no net force is in static equilibrium. ] The net force is due to the sum of forces acting on the object. • The forces (F) are vectors ] The SI unit of force is the newton (N)

Scalar Quantities ] Any measurement that consists of a single number is a scalar. • • ] 72 °F 500 milliliters 2. 54 centimeters 6 hours, 24 minutes (consider this as 6. 4 h) Most measured quantities consist of only a single magnitude.

Vector Quantities ] A measurement that requires more than one value to describe it is a vector. • • • ] ] 10 km to the northeast At 41. 9° N latitude and 88. 7° W longitude 15 pounds of force directed down These quantities can be thought of as carrying the value from a starting point to a destination. The word vector means carrier.

Vector Diagram ] One representation of a vector is an arrow. ] The tail shows the start of the vector. ] The tip points in the direction. ] The length of the arrow shows the magnitude. tip: direction length: magnitude tail: start

Parallelogram ] ] ] Force vectors act on a common object at a single point. If two vectors are added from a common origin one can be shifted to make a parallelogram. This is the same as putting the tail to the tip. C = 4. 6 N B = 3. 0 N A = 2. 0 N arrows over variables mean vectors

Gravity at Rest ] The force of gravity (FG) acts on all objects all the time. ] If an object is at rest, the law of inertia says that the net force is zero. ] There must be a force opposite to gravity that cancels it out. F = -FG FG

Support Force ] The force that opposes gravity for objects on the ground is called the support or normal force (FN). ] It is perpendicular (normal) to the plane of the ground. ] These are the only two forces acting on the object. FN FG

Support Force and Weight ] The support force pushing up against gravity can be measured. ] We measure weight with a scale that measures support force. ] Weight is a force, not a mass. ] Pounds measure weight, so force can be measured in pounds. Pearson Education

Tension Force ] ] A taut rope has a force exerted on it. If the rope is lightweight and flexible the force is uniform over the entire length. This force is called tension (FT) and points along the rope. Tension acts on both ends. FT forces on the rope FT = -Fg -FT forces on the ball Fg

Static Equilibrium ] An advertising sign weighs 210 N. It is supported from a post with a horizontal beam, and by a chain making an angle of 35 from the horizontal. ] Draw a diagram of forces on the sign. • Weight (W) is the force of gravity on an object. q = 35º I. Newton Esq. W = 210 N

Vector Forces ] With no motion, forces must sum to zero. ] Identify forces on the sign. • C is the force on the chain • B is the force on the beam • W is the weight • Free body diagram ] Vector sum is zero.

Pulley Lift ] A weight is lifted at a constant speed by a pulley. • Two forces on the block: gravity and tension • Two forces balance: FT = FG ] The tension force is equal along the rope. ] The forces balance at rest and at constant speed! force exerted on the rope FT FT FG 2 forces on the block

Friction Force ] At rest there must be a force that holds the object in place – friction (FF). ] Static friction is from the contact of resting objects. ] Sliding and rolling friction is from the contact of moving objects. FN FF m q FG

Constant Velocity ] Dynamic equilibrium applies in states of constant, nonzero velocity. v 0 • Vector forces balance in each direction ] A diagram shows the forces. • Horizontal: push, friction ] The forward horizontal force is the same magnitude as the resisting friction. FN FF Pearson Education FG Fhorizontal Fvertical