Physics Chapter 1: Motion and Momentum Section 1: What is Motion?

Vocab Physics Distance Displacement Speed Average Speed Instantaneous Speed Velocity

What is Physics??? Everything in the universe has an effect on every other thing Physicists study those forces and effects It is a science that relates to all other sciences Physics: The science of matter and its motion

Famous Physicists Benjamin Franklin Galileo Michael Faraday Sir Issac Newton Lord Kelvin Marie Curie Neils Bohr Albert Einstein Sheldon Cooper Leonard Hofstadter

Matter in Motion All matter is constantly in motion –The earth is spinning on its axis at 1,038 miles per hour and 66,660 miles per hour in its revolution around the sun –Because of this everything on its surface is always moving at those speeds even if it feels/looks like it is standing still

Changing Position To describe an object in motion you must first be able to prove that the object is in motion (moving) In physics, we can say something is moving if it is changing position –If an object moves from one location to another, it is changing position

Relative Motion Determining whether something changes position requires a point of reference –An object changes position if it moves relative to a reference point

You can tell the dog from the first picture has moved in the second picture because the dog’s position has moved relative to the ball (reference point)

Distance and Displacement Distance: How far you have traveled –Unit: meters or m Displacement: The direction and difference in position between your starting point and ending point –Unit: meters or m and direction

Distance = Displacement = 40 m East 40 m

Distance = Displacement = 50 m Northeast 70 m

Distance = Displacement = 0 m 140 m

Speed Speed: The distance traveled divided by the time taken to travel the distance –Unit: meters per second or m/s Speed = distance time

Speed can also be represented like this: d= distance r = rate (speed) t = time This means: –d ÷ t = rate –d ÷ r = time –t x r = distance d tr

Average Speed Average Speed: Total distance traveled by the time taken –Unit: meters per second or m/s Average Speed = total distance total time

Instantaneous Speed: The speed of an object at one instant in time –Unit: meters per second or m/s Instantaneous Speed = distance time

The average speed of each ball is the same from 0 to 4 seconds The first ball is moving at a constant speed. In each second, the ball moves the same distance. The second ball has a varying speed. It’s instantaneous speed is fast between 0 and 1 second and slow between 2 and 3 seconds.

Graphing Motion (speed) The motion (speed) of an object can be represented with a distance-time graph –Horizontal axis (X axis) = time –Vertical axis (Y axis) = distance –A horizontal line means no change in position occurs (no movement, speed = 0 m/s) –A steeper line represents a greater speed

Which student is traveling faster?Student A

Velocity Speed tells you how fast you are traveling but it is also helpful to know which direction you are traveling in Velocity: Speed of an object and the direction of its motion –Unit: meters per second or m/s and direction The velocity of an object can change if the object’s speed and/or direction of motion changes

Physics Chapter 1: Motion and Momentum Section 2: Acceleration

Vocab Acceleration Positive Acceleration Negative Acceleration

Acceleration and Motion When an object changes its motion it is accelerating –This is true even when the object is slowing down or stopping! Acceleration: The rate of change of the velocity –Unit: meters per second squared or m/s 2 Acceleration =  velocity  time –  = change in

Speeding Up Imagine you get on a bicycle… –The bike accelerates because your speed increases –When you stop accelerating you will have reached a constant speed –Speeding up = direction of acceleration is in the same direction the object is traveling direction of accelerationdirection of motion

Slowing Down While you are riding your bike you apply the brakes… –Your speed changes as you slow down –Because your speed changes you are accelerating –Slowing down = direction of acceleration is in the opposite direction the object is traveling direction of motionDirection of acceleration

Changing Direction While riding your bike you turn the handle bars: –Because you turn your bike your direction changes –Because you changed direction you are accelerating –Changing direction: the acceleration is at an angle to the direction of motion

Calculating Acceleration If an object is moving in a straight line, you can calculate its acceleration with this formula: Acceleration = final speed – initial speed time

Positive and Negative Acceleration Positive Acceleration –Speeding Up –Final speed will be more than your initial speed Negative Acceleration –Slowing Down –Final speed will be less than your initial speed

Graphing Accelerated Motion Accelerated motion can be represented on a speed-time graph –Horizontal axis (X axis) = time –Vertical axis (Y axis) = speed –A horizontal line means no acceleration (constant speed) –When the line rises, the object is speeding up (positive acceleration) –When the line falls, the object is slowing down (negative acceleration)

Which line is positively accelerating? Which line is negatively accelerating? Which line is not accelerating? Line A Line C Line B Label these lines on the graph in your notes!

Physics Chapter 1: Motion and Momentum Section 3: Mass and Inertia

Vocab Mass Inertia Momentum Law of Conservation of Momentum

Mass and Inertia Mass: The amount of matter in an object –Unit: kilogram or kg –Size/weight is NOT the same as mass Weight: how much something weighs –Can change: Your weight on Earth is different than it is on the Moon. Your mass is the same. Weight is NOT the same thing as mass!!! –The more mass an object has the harder it is to slow it down, speed it up, or change its direction

Inertia: Tendency of an object to resist a change in its motion –Objects with more mass = more inertia –The “Great Table Cloth Trick” Objects don’t fall because of inertia

Which object has more mass? Which object has more inertia? Which object would be harder to stop? Truck

Momentum Momentum: A measure of how hard it is to stop an object –Depends on the mass and velocity –More mass/high velocity = more momentum –Unit: kg · m/s say: kilograms multiplied by meters per second –Momentum = mass x velocity OR p=mv p vm

Conservation of Momentum Law of Conservation of Momentum: The total momentum of objects that collide with each other is the same before and after the collision –Ex. Billiard balls When the cue ball hits the other balls the motion of all of the balls changes The cue ball stops moving and other balls begin to move because the momentum from the cue ball was transferred to them

Using Momentum Conservation There are many ways collisions can occur: 1.Objects can bounce off of each other Ex. Bowling ball and pins 2.Objects can stick together Ex. Two football players during a tackle

Predicting Results of Collisions The Law of Conservation of Mass can be used to predict outcomes of collisions between different objects The results of the collisions depend on the masses of the objects

When an object with less mass strikes an object with more mass –The object with less mass bounces off in the opposite direction. The object with more mass moves in the same direction the object was initially moving

When an object with more mass strikes an object with less mass –Both objects move in the same direction after the collision. The object with less mass moves faster than the object with more mass

When two objects with the same mass strike each other –Both objects bounce off of each other and move in opposite directions after the collision