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Motion Describing Motion Motion Occurs when an object changes position Don’t have to see to know that it occurs Motion Motion can be describe by Speed, Velocity, Acceleration of an object. Frame of Reference Stationary (Not Moving) Reference Point Starting place (where the zero value is) Frame of Reference Examples Earth Most common frame of reference Tree House Stars Frame of Reference Teacher Domain http://www.teachersdomain.org/resource/ lsps07.sci.phys.fund.frameref/ Distance How far an object has moved Displacement Distance and Direction of an objects change in position from the starting point to ending point. Displacement Flash Interactive http://www.upscale.utoronto.ca/GeneralI nterest/Harrison/Flash/ClassMechanics/ DisplaceDistance/DisplaceDistance.html Distance and Displacement A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. Distance and Displacement A physics teacher walks 4 meters East, 2 meters South, 4 meters West, . 1. What is the total distance? 2. What is the displacement? and finally 2 meters North Displacement 1. What is the displacement of the crosscountry team if they begin at the school, run 10 miles and finish back at the school? Answer: zero because the displacement is measured from the starting to ending point. Displacement and Distance A student walks 3 blocks south, 4 blocks west, and 3 blocks north. What is the displacement of the student? 1. 10 blocks east 2. 10 blocks west 3. 4 blocks east 4. 4 blocks west 3 blocks north Answer: 4 blocks west 3 blocks south 4 blocks west Quick Review 1. A moving object passes a still object. Which one is the frame of reference moving or still object? 2. The ______ from point A to point B is 5 cm. Rates Rate – any change over time Different Rates Speed/Velocity Acceleration Speed Speed - The distance an object travels per unit of time. Rate – any change over time distance speed = time d s= t Types of SPEEDS Constant Speed stays the same Average Total distance traveled divided by the total time traveled Instantaneous Speed at a given point in time Velocity Speed in a given direction d v distance velocity = time d v= t t Graphing Motion Figure 1 Speed vs. Velocity Figure 2 Quick Write: Which one of the following figures shows the car slowing down? Explain why? Speed vs. Velocity Quick Write 1. 2. The speed and direction in which an object is moving is called? What is the formula for velocity? Example of Speed: If a frog jumps a distance of 3 m in 6 seconds, what is its speed? d = 3 m t = 6 sec v = d v=? t v = 3 m / 6 sec = 0.5 m/sec Example: A toad jumped 3 km in 1 hour, then jumped 1 km in 2 hours, it rested for 1 hour, and then jumped 5 km in 2 hours. What was the toad’s average speed? d = 3 km + 1 km + 5 km = 9 km t = 1 hr + 2 hr + 1 hr + 2 hr = 6 hr d v = v=? t v = (9 km) / (6 hr) = 1.5 km/hr NOTE: The time the toad stopped is included in the total time. Average Speed d v t A runner completed the 100.-meter dash in 10.0 seconds. Her average speed was 1. 0.100 m/s 2. 10.0 m/s 3. 100. m/s 4. 1,000 m/s Answer: 10 m/s because v= d = 100m =10m/s t 10s Instantaneous Velocity Which of the follow sentences contains an example of instantaneous velocity? (A) “The car covered 500 kilometers in the first 10 hours of its northward journey.” (B) “Five seconds into the launch, the rocket was shooting upward at 5000 meters per second.” (C) “The cheetah can run at 70 miles per hour.” (D) “Moving at five kilometers per hour, it will take us eight hours to get to the base camp.” (E) “Roger Bannister was the first person to run one mile in less than four minutes.” Speed Practice Problems 1. What is the speed of a car that travels 180 km in 1.5 hours? 2.What is the average speed of a dog cart that travels 2 km in the first 30 min., 0.5 km in the next hour and 3 km in 30 min.? 3.If a car has a constant velocity of 80 km/hr, how far will it travel in 5.5 hr? 4.If you walk at a speed of 2 km/hr, how long will it take you to walk 18.8 km? 5.If a lion runs 40 km/hr for 120 min, how far will it travel? 6.The train was traveling west at 200 km/hr. How long will it take the train to go 3600 km? Brain Pop Movie Acceleration http://glencoe.mcgrawhill.com/sites/0078802482/student_vie w0/brainpop_movies.html# Acceleration The rate of change of velocity velocity acceleration = time v a= t vf - vi a= t Δv a = Δt Δ v = vf - vi Δ v = change in velocity vf = final velocity vi = initial velocity Units m/sec m/sec m/sec Δ t = tf - ti Units t = time interval tf = final time ti = initial time sec sec sec Types of Accelerations Constant Acceleration stays the same Average Total velocity divided by the total time Instantaneous Acceleration at a given point in time Graphing Motion Example of Acceleration v a t A runner accelerates to a speed of 8.0 meters per seconds in 4.0 seconds. What was her acceleration? 1. 0.50 m/s2 2. 2.0 m/s2 3. 9.8 m/s2 4. 32 m/s2 Answer: 2.0 m/s2 because a=v = 8m/s = 2 m/s2 t 4s Example: What was the acceleration of a car that went from 0 kph to 90 kph in 60 seconds? v a= t Δ v = vf - vi a=? vf = 90 kph vi = 0 kph t = 60 sec = 1 min = 1/60 hr Δv = 90 kph - 0 kph = 90 kph a = (90kph) / (1/60 hr) = 5400 km/hr2 NOTE: 90 ÷ 1 = 90 x 60 = 5400 60 Acceleration Practice Problems 1.How long will it take a car to accelerate from 30 m/s to 90 m/s at a rate of 4 m/s2 ? 2.A truck is traveling at 90 kph suddenly slams on it brakes. After braking for 2 minutes, the truck reaches a speed of 30 kph. What is the trucks acceleration? 3.What is the change in velocity of a car that accelerates at 60 km/hr2 for 0.25 hr? 4. What is the final velocity of a truck that accelerated at 40 m/sec2 for 60 sec and has and initial speed of 30 m/sec? 5.How long will it take a skateboard traveling at 25 m/sec to stop if it accelerates at -4 m/sec2? 6.What is the acceleration of a ball that goes from 0 m/sec to 60 m/sec in 15 seconds? Force Push or pull that one body exerts on another A force can cause an object to move Different Types of Forces Net Force=(Total Force) Resulting combination of all forces acting on an object Balanced Forces (Equal Forces) Forces that are equal in size and opposite in direction Unbalanced Forces (Unequal Forces) Forces that are NOT equal in size or opposite in direction ALWAYS cause a change in motion Quick Write What are the three different types of forces? Define each forces. F= ma F Force Calculating force F=ma F = force m = mass a = acceleration Units kg·m/sec2 or N kg m/sec2 NOTE: one Newton (N) equal one kilogram meter per second squared. m a Friction Friction is an opposing (opposite) force in the direction in which the object is moving. Types of Friction Static=not moving Sliding Rolling Fluid Example How much force is exerted by a 2 kg baseball that is accelerating at 400 m/sec2? F = ? m = 2 kg a = 400 m/sec2 F=ma F = (2 kg)(400m/sec2) = 800 kg × m/sec2 = 800 N Force Practice Problems 1. A 3 kg baseball accelerates at 250 m/sec2. How much force is it exerting? 2. A 15 kg coconut hit the sand with 220 kg*m/sec2 force. What was the coconut’s acceleration? 3. 2900 N force is exerted by a truck on a compact car. If the truck has an acceleration of 2 m/sec2, what is the mass of the truck? 4. A car with a mass of 1000 kg accelerates through a green light at 4 m/s2. What is the net force on the car? 5. A person pushes a rock across the ground with a force of 60 N. The rock has a mass of 40 kg, what is the acceleration of the rock? Newton’s Laws of Motion 1st Law (Law of inertia) An object moving at constant velocity keeps moving at that velocity unless a net force acts on it V=20m/s V=10m/s F=10N Newton’s Laws of Motion I. Newton’s First Law of Motion An object in motion remains in motion. An object at rest remains at rest. Also known as the Law of Inertia Inertia The tendency of an object to resist any change in its motion Law of Inertia An object in motion will remain in motion unless acted on by an outside force An object at rest will remain at rest unless acted on by an outside force Newton’s Law of Motion 2nd Law (F=ma) The net force acting on an object causes the object to accelerate in the direction of the net force 3rd Law For every action there is an equal but opposite reaction Brain Pop Movie Newton’s Three Laws http://glencoe.mcgrawhill.com/sites/0078802482/student_vie w0/brainpop_movies.html# Gravity Gravity a force between two objects. Gravity causes an object to accelerate towards Earth. Weight Force of gravity acting on an object W=m*g W=kg*m/s2 Quick Write Name Newton’s Three Law’s of Motion. Calculating weight Fw = m g Fw m g FW = m g FW = weight m = mass g = acceleration due to gravity Units N or kg · m/sec2 kg m/sec2 NOTE: The acceleration due to gravity on Earth is 9.8 m/sec2. Example: What is the weight of a 100 kg man on Earth? FW = m g FW = ? m = 100 kg g = 9.8 m/sec2 FW = (100 kg)(9.8 m/sec2) = 980 kg m/sec2 = 980 N 1. What is the weight of a 22 kg object on Earth? 2. An apple drops from the tree with a mass of 112kg. What is the weight of the apple? 3. If an astronaut has a mass of 100kg, what is his weight on Earth where the acceleration due to gravity is 9.8m/s2. 4. An object on Earth is moving with a weight of 10 N, what is the mass of the object? 5. If an astronaut with a mass of 88kg weighs how much in kg*m/s2. Momentum 1. Relates to the amount of energy an object has. 2. Relates to the force needed to stop an object. 3. Depends on the mass and velocity of the object. Calculating momentum p= mv p p=mv Units p = momentum m = mass v = velocity m kg × m/sec kg m/sec NOTE: Units can vary. v Example: What is the momentum of a 1000 kg car goin 90 km/hr? p=mv p=? 1000 kg v = 90 km/hr 1 hr = 60 min 1 min = 60 sec 1 km = 1000 m p = (1000 kg)(90 km/hr)(1 hr/60 min) sec)(1000 m/1 km) = 25000 kg m/sec m= (1 min/60