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Transcript
C10, S1 – The Nature of Force What is a force? A ___________ or a _____________. Like velocity and acceleration, a _______________ is described by its _______________ and by the ________________ in which it acts. The strength of a force is measured in the SI unit called the _________________ (__). This unit is named after the scientist and mathematician Sir Isaac Newton. Direction and strength of a force can be represented by an arrow (___________). Determines whether an object ____________ and in what _____________. Combining Forces Typically, more than one single force acts on an object at one time. ________________– The _________________ of all forces acting on an object. DRAW THE THREE COMBINING FORCES EXAMPLES ON THE BOARD IN THE SPACE BELOW. Unbalanced Forces Whenever there is a ______ force acting on an object, the forces are _________________. Unbalanced forces can cause an object to __________________________, ______________________, or ______________________________. Example : Tug-of-War Balanced Forces ____________________ Forces – equal forces acting on one object in ______________________ directions. Each force is balanced by the other. Balanced forces acting on an object do ________ change an object’s ___________________. Net force is equal to _______________. Example Problem: Two people are moving a refrigerator. One person pushes with a force of 200 N and the other pulls with a force of 50 N. The force of friction between the ground and the refrigerator is 150 N. What is the net force acting on the refrigerator? Draw a model of this example and then solve for the net force. C10, S2 – Friction and Gravity Friction ________________ – The _____________ that two surfaces exert on each other when they _________ against each other. The strength of the force of friction depends on 2 factors: 1. _____________________________________________________ 2. _____________________________________________________ **Friction acts in a direction _________________ to the direction of the object’s ______________________ motion.** Types of Friction ____________ Friction – friction that acts on objects that are not moving. * In order to move an object, you must first overcome ___________________ friction. _____________ Friction – Occurs when two objects slide over each other. * Due to the _________________ __________________ between two surfaces. * Can be useful. __________________ __________________ ____________________ – Occurs when an object rolls across another surface. Is easier to overcome than _______________ friction. Engineers need to reduce the friction between the wheels and the rest of the object. Example: Pie plates with marbles- sliding/rolling _______________ friction – Occurs when a solid object moves through a ___________________ or _____________________. Easy to overcome unlike sliding friction. _______________ _______________ _______________ _______________ Gravity _____________ – A __________ that pulls objects toward each other. Sir Isaac Newton __________________________ – states that gravity acts between all objects in the universe. Factors that affect the force of gravity: ____________________ ____________________ _____________ – measure of the amount of _____________ in an object. The SI unit of mass is the ________________ (___). The _________ mass an object has, the ____________ gravitational force it has. Sun and the planets ______________________ Gravitational force depends on the ____________ between two objects. The farther two objects are apart, the ____________ their gravitational force. Orbital period of the planets around the Sun. Mercury (88 days), Venus (225 days), Earth (1 year), Mars (1.8 years), Jupiter (11.8 years), Saturn (29.4 years), Uranus (84 years), and Neptune (165 years) Weight and Mass Mass is the amount of matter in an object. _______________ is the amount of gravitational force acting on an object. Weight varies with the ________________ of the gravitational force but ________________does not. How are gravity and motion related? On Earth there are many forces that can act on objects, but what about space? In the absence of __________ (space/vacuum), objects are only affected by _____________________. ___________________ – when the only force acting on an object is gravity. In free fall, the force of gravity is an ________________ force which causes an object to _____________________ _________________ (32 ft/s²) - this is the ___________________ of an object due to gravity near Earth’s surface. Example: For every second an object is falling, its velocity increases by 9.8 m/s. Object is dropped from the top of a building Starting velocity 0m/s After 1 second velocity is 9.8 m/s After 2 seconds velocity is 19.6 m/s (9.8 + 9.8) After 3 seconds velocity is 29.4 m/s (9.8+9.8+9.8) And so on as it falls REGARDLESS OF MASS ALL OBJECTS IN FREE FALL ACCELERATE THIS WAY! Air Resistance _______________________ – type of fluid friction that objects falling through air experience. An _________________ force exerted on falling objects. Not the ____________ for all objects (__________________________). Balled up piece of paper versus a full sheet Air resistance _________________ with __________________ up to a point. Eventually the upward force will equal the downward force. _________________________ – the greatest velocity a falling object will reach. Weight of object _________________ the air resistance. Projectile Motion How does gravity effect objects that are moving horizontally? Figure 12 Objects that move _________________ fall at the same _________ as an object _____________________ straight down. If two objects are released at the same height at the same time they will hit the ground at the same time. How do you correct for this gravitational effect? C10, S3 – Newton’s First and Second Laws of Motion First Law of Motion ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ On Earth ________________ and ________________ are often the ______________________ forces that cause a change in an object’s motion. Inertia The tendency of an _____________________________________________. The first law of motion is also called the ____________________________. The amount of inertia an object has depends on the ______________ of the object. Second Law of Motion _____________________depends on the object’s ________________ and the _____________________ acting on the object. Acceleration = Net force / Mass ___________________, meters per second per second (m/s²) _________________, newtons (N) ________________, kilograms (kg) C10, S4 Newton’s Third Law of Motion 3rd Law of Motion The third law states – If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. “____________________________________________________________.” Action-Reaction Pairs Walking Jumping Birds flying Detecting Motion Not always possible to detect Inertia and size of the object Action-Reaction Forces _________________ cancel. These forces do not cancel because they are ___________________________________________________. FIGURE 16 Momentum Momentum is a characteristic of a moving object that is related to the mass and the velocity of the object. Momentum = mass X velocity Units – kg•m/s The more momentum a moving object has, the harder it is to stop. Law of Conservation of Momentum Law of Conservation of Momentum – states that, in the absence of outside forces, the total momentum of objects that interact does not change. **The total momentum of any group of objects remains the same, or is conserved unless outside forces act on the objects.** Momentum may be transferred from object to another, but none is lost. C10, S5 Rockets and Satellites Circular Motion – Objects moving in a circle are always ____________________. If an object is ____________________ a ____________ must be acting on it. _______________________ – any force that causes an object to move in a ________________ path. Gravity and Satellites