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Motion Notes Speed Momentum Acceleration and Force Friction and Air Resistance Newton’s Laws of Motion

I. Motion A. Speed and Velocity. 1. Speed: the distance traveled divided by the time interval during which the motion occurred. Since speed is a derived measurement.  SI unit is meter per second ( m/s ). When a car is moving at a speed that does not change over a period of time, it is called constant speed.

2. Speed can be determined from a distance-time graph 3. Speed can be calculated using distance and time. The equation for speed is:  speed = distance/time v = d / t Velocity: is the quantity describing both speed and direction. (Direction is the path of the motion: east, north, south, etc…) The equation for velocity is the same as speed, the only difference is that you must indicate the direction of the motion.

II. Momentum A. Momentum: a quantity defined as the product of an object’s mass and its velocity. (“power”). B. Momentum equation: momentum = mass X velocity p = m X v (p= momentum, m= mass, v = velocity) C. The law of conservation of momentum: The total amount of momentum in a system is conserved

III. Acceleration A. Def: Change in velocity divided by the time interval in which the change occurred. (How fast an object speeds up or slows down) B. Key points: 1. A change in direction will result in experiencing acceleration. 2. Units are m/s 2 Acceleration= final velocity-initial velocity time

3. Acceleration- indicates how fast a car is speeding up, or how fast is slowing down 4. Positive acceleration means an object is speeding up. 5. Negative acceleration means an object is slowing down. Ex. A car has a constant speed of 60 m/s and the person driving the car increases his speed to 100 m/s. If it takes him 7sec to reach this speed, what is his acceleration in m/s 2 ? Formula: a= V f -V i t Ex. A car can go from 0 to 96 m/s in 4 sec, what is its acceleration?

IV. Force Force A. Def: the cause of acceleration, or change in an objects velocity. Net force: is the combination of all the forces acting on an object. Balance forces: forces acting on an object that combine to produce a net force equal to zero. Unbalanced forces: forces acting on an object that combine to produce a net nonzero force.

V. Friction and Air Resistance A. Friction: the force between two objects in contact that opposes the motion of either object. B. Air Resistance: a form of friction, it is caused by the interaction between the surface of a moving object and the air molecules. What determines it amount of air resistance? 1. Size 2. Shape 3. Speed. Note: air resistance increases with as the objects speed increases.

VI. Gravity A. Def: the attraction between two particles of matter due to their mass. Gravity is a unique force; it does not have to be touching the object to exert its force. B. Mass and distance affect gravitational force. 1. As the distance between two objects increases the gravitational force decreases, and vice-versa. 2. The force of gravity is proportional to their mass and inversely proportional to the square of the distance between them.

Newton’s Laws of Motion

Newton’s First Law Newton’s 1st Law: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Inertia: is the tendency of an object to remain at rest or in motion with a constant velocity.

Newton’s 2nd Law Newton’s 2nd Law: The force of an object equals its mass times its acceleration. F=m X a The unit for force is Newton (N). 1N=1kg X 1m/s 2 Practice problem: What is the force necessary to accelerate a 1250 kg car at a rate of 40m/s 2 ?

Free Fall and Weight Def: the motion of a body when only the force of gravity is acting on it. Free-fall acceleration near Earth’s surface is constant. Note: in this class we will disregard air resistance for all calculations. Gravity acceleration on any object is 9.8 m/s 2. Weight equals mass times free-fall acceleration weight=mass x free-fall acceleration  w=m X g Weight is the force on an object due to gravity. Because weight is a force, the SI unit of weight is the Newton (N).

Weight is different from mass a. mass is a measure of the amount of matter in an object b. weight is the gravitational force an object experiences due to its mass. Ex: 66 kg x 9.8 m/s 2 =650 N (Earth 150 lb) 66 kg x 1.6 m/s 2 = 110 N (moon 24 lb) Weight influences shape Terminal Velocity: the maximum velocity reached by a falling object that occurs when the resistance of the medium is equal to the force of gravity. The object has stopped accelerating at this point.

Newton’s Third Law Newton’s Third Law: for every action force, there is an equal and opposite reaction force. Ex. When you kick a soccer ball, the force exerted by your foot is the action force, the ball also exerts a force on your foot, this is the reaction force that is equal to the action force.

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