Motion

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

Speed activity

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

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

MOTION

• Distance the length of a path between two points.

–Si units:(METRIC) km, m, mm, cm, etc.

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

• 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?

• 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.

Answer

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

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.

Velocity and Acceleration

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

Graphing Motion

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

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.

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

• 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.

Calculating Acceleration

Vf = final velocityVi = initial (starting) velocity

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

non linear graph

Newton’s law’s

• P. 280 1st law• P. 282 2nd law• P. 284 3rd law

• Crash test dummies

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 ____

• 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/s2). –1 N = 1 kgm/s2

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…

FORCE

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

change in motion

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

• 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.)

GRAVITY

• Gravity – force that attracts or pulls objects together–Acts downwards toward

center of Earth–Causes objects to accelerate

as they fall

Newton’s Laws

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

Newton’s Laws

• 1st 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.

Newton’s Laws

• 2nd – 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

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/s2?• What is the force on a 80 kg

box accelerating down a ramp at 2 m/s2?

Newton’s Laws

• Mass – measure of inertia, amount of matter in an object• Weight- force of gravity on an

object

• This formula is a substitute for F= (m)(a)…– g = 9.8 m/s2 (on earth)

• Units for weight = newtons (N)b

Newton’s Laws• 3rd – 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)

MOMENTUM

•Momentum - describes how mass and velocity are affected by each other.

• units are kgm/s

•No velocity? no momentum!

•Conservation of momentum-

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