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Motion p.272 -273 in red text #13.1 worksheet accelerated Speed activity

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MOTION motion change in your position compared to a frame of reference. – as a train moves past a platform, people on the platform see those on the train speeding by. when people on the train look at one another, they don't seem to be moving at all OR moving backwards

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MOTION frame of reference - comparing an object’s motion to another object –Your house stays still as the cars drive past –a frame of reference is necessary in order to describe motion

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MOTION Distance the length of a path between two points. –Si units:(METRIC) km, m, mm, cm, etc.

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MOTION Speed distance traveled per unit of time – S = d/t – A car travels 70 km per hour – Choose units that make sense: m/s, km/h

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Average speed- the total distance traveled, d, divided by the total time, t, it takes to travel that distance. speed= distance/time Ex- on vacation: 60 km in 0.8 hr, and 35 km in 0.5 hr. What is your average speed?

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Instantaneous speed the rate at which an object is moving at a given moment in time –Speedometer in a car **Average speed is computed for the entire duration of a trip, and instantaneous speed is measured at a particular instant.

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Answer S= d/t 60 km + 35km = 95km.8hr +.5hr = 1.3hr S= 95/1.3=73km/hr

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Speed Activity In class or track: Run a predetermined distance, measure time with a top watch. Two trials each. Any motion you choose. Calculate speed for you and your partner. Calculate speed for your group. Calculate speed for the class.

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Velocity and Acceleration P. 274-275 in red text #13.2 accelerated #11.2 honors Velocity and acceleration enrichment

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Graphing Motion The slope of a line on a distance-time graph is speed.

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Velocity Velocity- the speed and direction in which an object is moving –Sometimes you need to know the direction…If two trains are traveling… Velocity is a vector.

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Acceleration Acceleration - The rate of change in velocity –Changes in speed, direction or both – Can Increase or decrease, (be positive or negative) – acceleration = zero if it is moving at the same speed in thesame direction

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Constant acceleration is a steady change in velocity over time. –the velocity of the object changes by the same amount each second –A jet taking off. –A rollercoaster dropping down the first hill.

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Calculating Acceleration Vf = final velocity Vi = initial (starting) velocity

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Graphing Acceleration The slope of a speed-time graph is acceleration Can be linear or non linear graph

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Newton’s law’s P. 280 1 st law P. 282 2 nd law P. 284 3 rd law Crash test dummies

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Force force is a push or a pull that acts on an object. –can cause a resting object to move –can accelerate a moving object Acceleration =changes in ____ and/or ____

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Newtons(N)- unit for force One N is the force that causes a 1 kg object to accelerate at a rate of 1 meter per second every second (1 m/s 2 ). –1 N = 1 kgm/s 2

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FORCE NET FORCE – Combination of forces in the same direction or opposite directions Ex. If two people are pushing a cart at the same time…

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FORCE Balanced force- when forces are balanced, net force = 0. No change in motion (arm wrestle) Unbalanced force- causes a change in motion

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FRICTION Friction – force that opposes the motion of objects by contact – Static – Sliding – Rolling – Fluid – http://www.planet-science.com/text_only/under_11s/friction.html

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Paradoxically, friction is one of those things that's so prevalent, so ubiquitous, that it's hard to think of any. But here are a few that come immediately to mind: 1. Air resistance: friction between a moving body and molecules of air. 2. Rubbing: Rubbing your hands together to create warmth. 3. Tire traction: the friction between the tires and the surface of the road that allows your car to accelerate, slow down, and negotiate turns and corners. 4. Static friction: the friction between two surfaces that prevents items on less-than-perfectly-level tables and shelves from sliding off. Also, the friction between the soles of your shoes and the ground that permits you to walk without busting your butt. (Similar to 3 and 4.) Paradoxically, friction is one of those things that's so prevalent, so ubiquitous, that it's hard to think of any. But here are a few that come immediately to mind: 1. Air resistance: friction between a moving body and molecules of air. 2. Rubbing: Rubbing your hands together to create warmth. 3. Tire traction: the friction between the tires and the surface of the road that allows your car to accelerate, slow down, and negotiate turns and corners. 4. Static friction: the friction between two surfaces that prevents items on less-than-perfectly-level tables and shelves from sliding off. Also, the friction between the soles of your shoes and the ground that permits you to walk without busting your butt. (Similar to 3 and 4.)

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GRAVITY Gravity – force that attracts or pulls objects together – Acts downwards toward center of Earth – Causes objects to accelerate as they fall

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Newton’s Laws 1 st - An object at rest remains at rest OR an object in motion remains in motion,unless acted on by an outside force

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Newton’s Laws 1 st law is called the Law of Inertia. Inertia- tendency of object to resist change in motion. – seat belts, airbags, etc – these objects protect you from inertia.

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Newton’s Laws 2 nd – the acceleration of an object depends on the force acting on the object and the mass of the object F= (m)(a) OR a= f / m

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PRACTICE F = (m)(a) How much force is required to move a car with a mass of 1200 kg at a rate of 3.0 m/s 2 ? What is the force on a 80 kg box accelerating down a ramp at 2 m/s 2?

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Newton’s Laws Mass – measure of inertia, amount of matter in an object Weight- force of gravity on an object

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This formula is a substitute for F= (m)(a)… – g = 9.8 m/s 2 (on earth) Units for weight = newtons (N)b

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Newton’s Laws 3 rd – for every action or force, there is an equal and opposite reaction or force – Bumper cars – If the forces both act on the same object the object will not move (net force = 0)

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MOMENTUM Momentum - describes how mass and velocity are affected by each other. units are kgm/s No velocity? no momentum!

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Conservation of momentum- The loss of momentum in one object is the gain of momentum in another

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