Forces
Force - a push or a pull A force described by its strength and by the direction in which it acts The SI unit for force is the newton (N)
The direction and strength of forces can be represented by arrows; the longer the arrow, the stronger the force
Balanced forces - forces that are opposite in direction and equal in strength create no change in motion net force equals zero
Tug-of-war with balanced forces Net force = 0
Arm wrestling with balanced forces Net force = 0
Unbalanced forces - forces that produce a nonzero net force always cause a change in motion cause an object to begin moving, stop moving, or change direction and/or speed
If the forces are in opposite directions, the net force is the difference between the two forces.
Tug-of-war with unbalanced forces
Arm wrestling with unbalanced forces
If the forces are in the same direction, the net force is the sum of the two forces. + =
Net Force - the combination of all forces acting on an object The net force will always be in the direction of the stronger of the two forces.
Friction - the force that one surface exerts on another when the two surfaces rub against each other opposes motion (acts in opposite direction) brings an object to rest produces heat
The strength of the force of friction depends on how hard the surfaces push together and the types of surfaces the objects have. In general, smooth surfaces produce less friction than rough surfaces.
Without friction, objects would continue moving until they strike another object.
Static Friction - friction that acts on objects that are not moving force is needed to overcome static friction to get an object moving once an object is moving, there is no longer any static friction
Sliding Friction - occurs when one solid surface slides over another examples: rug burn bicycle brakes sand on ice
Rolling Friction - occurs when an object rolls across a surface easier to overcome than sliding friction necessary for traction for cars, bikes, etc.
Ball bearings change sliding friction to rolling friction used in cars, skateboards, rollerblades, etc. to decrease the amount of friction between the moving surfaces
Fluid Friction - occurs when an object moves through a fluid Fluids include water, oil, and air
Lubricants change sliding friction into fluid friction include oil, grease, and wax
Aerodynamics Engineers design cars, trains, airplanes, etc. to decrease fluid friction Decreases the amount of energy required to reach a desired speed; increases efficiency of vehicle
Benefits of friction - tire tread, shoe tread, brakes, sand on icy roads, fingerprints
Gravity - a force which pulls objects toward each other
Law of Universal Gravitation -
Law of Universal Gravitation -
Law of Universal Gravitation -
Mass - a measure of the amount of matter in an object does not change from place to place
Weight - a measure of the amount of gravitational force exerted on an object changes from place to place
Free Fall - occurs when the only force acting on a falling object is gravity gravity causes a falling object to accelerate as it falls to the Earth Acceleration due to gravity on Earth = 9.8 m/s 2
Air Resistance - fluid friction experienced by objects falling through the air
Air resistance increases as the surface area or velocity of an object increases
Terminal velocity - the greatest velocity a falling object can achieve upward force of air resistance is equal to the downward force of gravity (balanced forces) the object stops accelerating**
Projectile - any object that is thrown into the air object has forward inertia and is being pulled down by gravity; this causes the projectile to move in an arc which is called projectile motion
If one object is dropped vertically and another is thrown horizontally, both objects will hit the ground at the same time.*
Newton s First Law of Motion - an object at rest will stay at rest, and an object in motion will stay in motion, unless it is acted upon by an unbalanced force; AKA The Law of Inertia
Inertia - the tendency of an object to resist any change in its motion The more mass an object has, the greater its inertia and vice versa
Newton s Second Law of Motion - acceleration depends on the object s mass and on the net force acting on the object Force = Mass X Acceleration (F=ma) Acceleration = Force/Mass *
F = mass (kg) x acceleration (m/s²) 1 kg m/s² = 1 Newton Weight = mass x acceleration due to gravity (N) (kg) (m/s²)
If Mr. Lane can accelerate at a rate of 5 m/s² and has a mass of 115 kg, how much force can he generate when he tackles someone? F = ma F = 115 kg x 5 m/s² F = 575 kg m/s² F = 575 N
If Mr. Fronk tackles someone with a net force of 480 N and has a mass of 80 kg, what is his acceleration? F = ma a = F/m a = 480 kg m/s² 80 kg a = 6 m/s²
If Mr. Palmer is accelerating at a rate of 5 m/s² and has a net force of 425 N, what is his mass? F = ma m = F/a m = 425 kg m/s² 5 m/s² m = 85 kg
Newton s Third Law of Motion - for every action there is an equal and opposite reaction
Momentum - mass x velocity p = mv kg m/s
What is the momentum for a 6 kg bowling ball traveling down the bowling lane at a rate of 5 m/s? p = mv p = 6 kg x 5 m/s p = 30 kg m/s
What is the mass of a bowling ball that travels at a rate of 5 m/s and has a momentum of 20 kg m/s? p = mv m = p/v m = 20 kg m/s 5 m/s m = 4 kg
What is the velocity of a 5 kg bowling ball that has a momentum of 35 kg m/s? p = mv v = p/m v = 35 kg m/s 5 kg v = 7 m/s
The Law of Conservation of Momentum - in the absence of outside forces, the total momentum of objects that interact does not change