Quinlan Physics While most people know what Newtons

Quinlan Physics

� While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean).

� Born 1642 December, 25 � Calculus � Gravity � 3 Laws of Motion � Alchemy � Theology

� 1 st Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force. (Inertia: Resists change) � 2 nd Law – Force equals mass times acceleration. (F= m x a) � 3 rd Law – For every action there is an equal and opposite reaction. (Action/Reaction)

Newton’s 1 st Law – class demo � Inertia: the ability of an object to resist change � Net Force: the total force of a system � Mass: the amount of matter in an object � Force: something that is capable of changing an object’s state of motion � If it has mass it has inertia…

� An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.

�Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. � These apples will not move unless acted on by an unbalanced force.

� Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

� Unless acted upon by an unbalanced force, this football would sit on the tee forever.

� Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? � It’s a force we sometimes cannot see – friction.

� Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction. � Cleats give us extra friction on the grass!

� Forces acting on a body � Examples of Cone

� Balanced forces occur when Fnet= 0 N � Unbalanced forces occur when Fnet = 0 N

� Weight: the force due to the acceleration of gravity � Fw= m(g)

� Emilio is driving a Tacoma which is towing a trailer with a constant force of 440 N. If the total mass of the trailer and its contents are 275 kg, what is the trailer’s acceleration and direction?

� Newton identified force as the cause of motion (Hect) �F = m x a � Action-Reaction means all forces occur in pairs � Forces are VECTORS!

� Push/Pull � Electrical � Magnetic � Nuclear � Gravity �As weight � Friction � We will deal with primarily contact forces here! � These are “action at a distance” forces- move mysterious

� Push o’ war with the chair � Clearly, the stronger force wins � Concurrent Forces- Forces acting on the same point at the same time � Net Force= the sum of Concurrent Forces= the Resultant Force

� Free 120 N Fs=120 N Body Diagram (FBD) � Simplifies Picture � Centralizes mass 100 N Fp=100 N Fnet=20 N

�A drag racer screams along at 190 mph, its engine is delivering a force of 40, 000 N and a friction of 770 N. The parachute accidentally deploys, adding 2975 N of drag. Find the net force. Use FBD. Is the car still speeding up? � Fnet=36, 255 N

� Read section 4. 5, including the “Harrier”, sample problems and solutions. � Then skip to example 4. 8 pg. 121 -122 � Watch http: //kevandang. textamerica. com/? r=34750 57

� Fn is called the normal force �It means it is perpendicular to the surface being used �Θ will usually be less than Fn*Fw � Fn= Fw*cos(Θ) � Fp= Fw*sin(Θ) �P means it is parallel to surface

� Equilibrium- state of motion where acceleration = 0 � Translational Equilibrium- a=0, all forces in balance. (Can be rotating at constant speed. ) � Equilibrant Force- The force that operates opposite to the resultant force of a system, causing it to slow down.

� Moving and groovin’ with a spring scale �Lifting �Pulling �Angled � Statics- The study of equilibrium, using reaction forces through supports to cancel forces. � 1 st true engineering class!!!!

� The table weighs 200 N. It has 162 N of boxes centered perfectly on the table. Find the weight supported by each leg. Use a FBD.

� Let’s combo force and F=m x a concept. � The Mine excavator with the coal…

� Calculate the acceleration, and FT

� Try it on your own � In your lab book write forces in 2 D � Select: -car -pulley -string -a mass � Calculate the acceleration going off the side of the table and solve the FBD for your system.

� Weighed down on two sides

� In an Atwood's machine experiment, the larger mass is 1. 8 kg and the smaller mass is 1. 2 kg. � Ignoring friction, what is the acceleration of the masses? � What is the tension in the string?

The net force on each mass is given in the two equations � 1. 8 a = 1. 8 g -T � 1. 2 a = T - 1. 2 g � Since a and T are the same for both masses, add the two equations: � 3. 0 a =. 6 g � a =. 2 g = 1. 96 m/s^2 � Substituting for a in the first equation: � 1. 8(1. 96) = 1. 8(9. 8) - T � T = 14. 1 N �

� An elevator has a mass of 1150 kg and the elevator has a counterweight with the mass of 1000 kg. Find the acceleration and Tension Force.

� Jack and Jill ran down the hill, carrying a 10 kg pail of water. The they held created a 60 degree angle. Calculate the tension in the rope.

�A 20. 0 kg mass is pulled by along a surface by a horizontal force of 100 N. Friction is 20. 0 N. What is the acceleration of the mass? � Sum of forces (vertical forces cancel as evidenced by lack of acceleration in the vertical dimension) � Fnet = T + Ff Fnet = (100 N) + (-20. 0 N) = 80 N

�A 49 -N block is pulled by a horizontal force of 50. 0 N along a rough horizontal surface at a constant acceleration of 6 m/s^2. What is the coefficient of friction?

� In the vertical axes forces are equal and opposite as there is no vertical acceleration. � FN = -Fg � FN = mg = 49 N � m = 49/9. 81 = 4. 99 kg

� In the horizontal axis � Fnet = T + Ff � Fnet = (50 N) + Ff Newton's Second Law: Fnet = ma � Fnet = (4. 99 kg)(6) = 30. 0 N � Ff=20 N

� Obviously, if forces are vectors, they can be resolved into components as well as added. � While the resolution of forces will not focus as much on the concepts of vertical and horizontal, the goal will be to create right triangles and ease the trigonometry.

� An 18 kg box is secured on an incline plane at an angle of 35 degrees by string that can support 97 N of force. �A. Show mathematically whether or not the string will hold. �B. If the string breaks and the block accelerates down the ramp, and if there is no friction, what is the acceleration of the box?

� Friction- a force that operates in the direction opposite to motion due to contact between surfaces. � Draw ridged surfaces

� 1. Lubrication-wax on snowboard � 2. Rollers � 3. Smooth Surfaces- air hockey table � 4. Reduce Weight-car, skis

�I push a lawn mower with 450 N of force. The handle forms a 35 degree angle with the ground. �What force do I push forward with? �What force do I push down with? � Find the normal force if the mover is 10 kg, find a is optional

� The 1500 kg truck is on a 40 degree incline. Find the acceleration down hill of the truck if the emergency brake is on and reset it.

� Studies have shown that even the smoothest surface can develop friction- mysterious, but most likely “sticky” electrical interactions between the molecules.

� Jack and Jill ran down the hill, carrying a 10 kg pail of water. The pail they held created a 60 degree angle between their arms. Calculate the tension in the rope.

� Ben is walking his 93 kg pot belly pig with a and pulling with a force of 120 N at 37 degree above the horizontal. What is the acceleration of the pot belly pig? What is the Normal Force?

�A baby elephant pulls a small tree with the mass of 30 kg with a force of 200 N at an angle of 30 degrees. Ignore friction, what’s the acceleration and Normal Force?