# Newton’s Laws of Motion (and force!!) A force is a push or pull on an object.

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Newton’s Laws of Motion (and force!!)

A force is a push or pull on an object

  control over movement:  desired motion  or preventing undesirable movement Apply Force:

Contact Forces   muscles   machines/mechanical   ropes and wires   Friction  adhesion EXAMPLES of forces:

EXAMPLES of FORCES:  Non-contact forces: Nuclear Electrical/magnetic Gravity  weight

Non-contact Forces such as gravity, magnetic, and electric forces. Non-contact Forces such as gravity, magnetic, and electric forces.

 Like Velocity and Acceleration….. FORCE has both magnitude AND Direction!!!

 NET FORCE (unbalanced force)  results in motion  for an object at rest)  or acceleration (a change in velocity)  For an object already in motion

 Equilibrant Force  Net Force = 0 …..means, an object at rest remains at rest OR an object moving with constant motion will continue at that constant motion.

 FORCE IS MEASURED IN NEWTONS One NEWTON (N)  1 kg x 1m s 2 Think about it…. Force = mass X acceleration  that gives a 1 kg object, an acceleration of 1m/s2

 Inertia  tendency of an object to RESIST a change in motion  Example: velocity of an object remains constant unless a force changes it   the greater the mass, the greater the inertia

Newton’s First Law of Motion An object continues in a state of rest or in a state of motion at constant speed along a straight line… unless compelled to change that state by a net force.  an object moving at a constant velocity remains at that velocity unless a NEW FORCE (>0) acts upon it

Inertia plays a central role in one type of seat belt mechanism.

Newton's First Law of Motion (inertia): Two mousetrap cars with different masses. which one has more inertia? Construction Tip: Wherever possible, remove mass = less energy required to overcome inertia and get your car moving. So More energy available to propel your car forward. Less mass = less inertia!

friction   Friction  force of adhesion   depends on the surface and force acting between surfaces  EXAMPLES OF FRICTION: air, fluid, solids

Examples of contact forces Describe what role Newton’s first law plays a role in what is occurring in this picture

The Normal Force & Friction

Newton’s Second Law of Motion When a net force F acts on an object of mass m, the acceleration a that results is directly proportional to the net force and is inversely proportional to the mass. If: net F = m X a then…. direction of acceleration = direction of the net force SI Unit of Force: kg m/s 2 = newton (N)

Newton’s second law and mousetrap cars: mass resists acceleration, and force causes acceleration. to double the acceleration of an object, double the force or remove mass.

F orce causes acceleration! N eed more pulling force? S horten the lever arm and move the mousetrap closer to the drive wheels. S hortening the lever arm implies moving the string closer to the hinge on the mousetrap.

ONCE AGAIN!!! A NEWTON ….is the amount of force required to accelerate a 1 kg object 1 m/s 2

m = 1850 kg With two guys pushing…….what are The net forces???

If the airplane’s mass is 13 300 kg, what is the magnitude of the net force that the catapult and jet engine exert on the plane?

The Normal Force

GRAVITY (gravitational force)   the pull an object exerts on another object   the amount of gravitational force is dependent on:  1) Mass of the two objects  2) distance between objects   the greater the mass, the greater the gravitational pull on that object   Weight  measure of gravitational force   varies dependent on proximity to EARTH

Weight vs Mass  Mass is the measure of… the matter of an object and an object’s resistance to change in motion

Newton’s Third Law of Motion Whenever a body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body.

Newton’s 3 rd Law……   action force = reaction force   for every action, there is an equal and opposite reaction!!  tires of a car push against the road, and the road in turn pushes back on the tires,  a swimmer pushes the water backward, and the water pushes swimmer forward

""A mousetrap car is propelled because the drive wheels push on the floorand the floor pushes back on the car [wheels]” TThe wheels can only push on the floor as hard as the floor can push back. If the floor cannot push back with the same force as the wheels push, then the wheels will spin in place and the car will not accelerate to its fullest potential.

Newton’s Third Law For every action there is an equal and opposite reaction.

Fortunately for sparky, Zeke knew the famous “Rex Maneuver”!

Free Body Diagrams A Free Body Diagram distills the problem’s complexity down to only those actions that are interacting with the object of interest.

Consider the following situation: You are standing in the middle of the room. Are there any forces acting on you? Is there net force acting on you? Draw the forces acting on you. Justify your answer by referring to Newton’s Laws.

Now remove the floor and draw the forces acting on you. What is your state of motion now? Characterize it by stating something that we can calculate.

Distance Car Tips: l onger lever arms l arger drive wheel(s), ideally 1-2 feet in diameter s mall drive axle s mall power output d ecrease mass and rotational inertia r emove ALL friction

Speed Cars shorter lever arms smaller drive wheel(s), ideally around 2-5" in diameter but no larger than a compact disc. If the wheel-to-axle ratio is too small, your vehicle will [spin out and] waste energy. Increase traction Larger diameter drive axle. You can get more torque with a thick axle--more torque means greater acceleration! Larger power output. For speed, the objective is [to quickly convert potential energy into kinetic energy.] Decrease mass and rotational inertia Remove ALL friction

Friction slows and stops the mousetrap car Energy moves the vehicle. too much friction = energy consumed too quickly and vehicle won’t travel far or accelerate fast. Check moving components and decrease the friction at each point. The more moving components, the greater the force of friction will be (usually. The smaller the frictional force, the farther your supply of energy will propel your vehicle. Slow-moving cars have a smaller force of air resistance and travel farther than faster-moving vehicles

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