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Explore the concept of motion, frame of reference, average speed, velocity, acceleration, and momentum in physics. Practice problems and examples included.
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Frame of Reference • Whenever you describe something moving you are comparing it to something that is not moving. • The thing that is not moving is the frame of reference. • It is usually the background.
Relationship between motion and frame of reference • Motion is any change in position over a certain amount of time. • Frame of reference depends on: • Type of movement • The position from which you are observing.
What is the frame of reference? • The sun is rising over the mountains. • The earth
Calculate average speed of an object. • Speed is the rate at which an object moves. • Formula: S = Distance / Time, s = D/T • Measured in meter/sec, m/s or km/hr • Average speed is the total distance divided by the total time. • Constant speed is the speed of an object at every point in it journey.
Graphing speed • Average speed • Total distance / total time • Meters / sec • Velocity • Speed in a given direction. • Velocity = distance / time • miles/hr west • The x axis is always labeled as time • The y axis is always labeled at distance.
Combining velocities • To combine velocities you add them together. • If a river is moving at 5 m/s and you are rowing at 12 m/s, what is your total velocity? • 17 m/s • What if the wind is blowing 50 mph and the plane is flying into the wind at 250 mph. What is the velocity of the plane? • 250 mph - 50 mph • 200 mph
Acceleration • The rate of change in velocity. • Formula • Accel. = Final Velocity - Original Velocity • Time • A roller coaster at the top of a hill has a velocity of 10 m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26 m/s. What is the acceleration of the roller coaster? • 26m/s - 10 m/s • 2 sec • 8 m/s/s or 8 m/s2
Practice Problems • A roller coaster is moving at 25 m/s at the bottom of a hill. 3 seconds later it reaches the top of the hill moving at 10 m/s. What is the deceleration of the roller coaster? • 5 m/s • A car is traveling at 60 km/hr. It accelerates to 85 km/hr in 5 seconds. What is the acceleration of the car? • 5km/hr/sec
Momentum • Momentum depends on the mass of an object and the velocity it is traveling. • If either mass or velocity is large then the object has a large momentum. • Momentum = mass x Velocity • g m/s • What is the momentum of a .30kg bluejay flying at 17 m/s? • 5.1 kg*m/s
Conservation of Momentum • The total momentum of any group of objects remains the same unless outside forces act on those objects. • Practice • What is the momentum if a skier has a mass of 60 kg and a velocity of 20m/s? • 1200kg*m/s • What is the momentum of an object that has a mass of 2 kg and a velocity of 4 m/s? • 8 kg m/s