3Motion and PositionA reference point is needed to determine the position of an object.Motion occurs when an object changes position relative to its reference point.Motion depends on its point of reference.Question – are you moving right now?
4Distance and Displacement Distance – how far an object has movedDisplacement – the distance and direction of an object’s change in position from the starting pointThe SI unit for distance and displacement is the meter (m).
5Distance and Displacement Example: A runner runs from the start line 50 m north plus 30 min the opposite direction.What is the distance?What is the displacement?50 m N30 m SSTART
6Speed Speed – the distance an object travels per unit of time Average speed – total distance traveled divided by the totaltime of travelInstantaneous speed – speed at a given point in timeRemember to use the metric system!m/s (meters/second) or kilometers/hourkm/h
7Velocity Velocity – includes the speed of an object and the direction of its motionBecause velocity depends on direction as well as speed,the velocity of an object can change even when its speeddoes not!Car is driving 30 km/hrbut it’s velocity is constantlychanging!
8Equation to Find SpeedSpeed (in meters per second) = distance (in meters) / time (in seconds)s = d/tUnits – meters/second (m/s) or kilometers/hour (km/h)
9Graphing Motion Motion can be shown on a distance vs. time graph Time on x-axisDistance on y-axisOn a distance vs. time graph the slope describes the speedSteeper slope = faster speedHorizontal line = zero speed = object at rest
11What Is Acceleration? Acceleration is the rate of change of velocity. When the velocity of an object changes, the object is accelerating.A change in velocity can be either a change in how fast something is moving or a change in the direction it is moving.So acceleration occurs when an object changes its speed, its direction, or both.
12Speeding Up and Slowing Down When you think of acceleration, you probably think of something speeding up. However, an object that is slowing down also is accelerating.Acceleration also has direction, just as velocity does.
13Speeding Up…If the acceleration is in the same direction as the velocity, the speed increases and the acceleration is positive.
14Slowing Down…If the speed decreases, the acceleration is in the opposite direction from the velocity, and the acceleration is negative.
15Changing Direction… Any time a moving object changes direction, its velocitychanges andit is accelerating.The speed ofthe horses in thiscarousel is constant,but the horses areaccelerating because theirdirection is changingconstantly.
22Force Force – a push or pull Sometimes it is obvious a force is being applied andsometimes it is notForces cause the motion of an object to changeForces are measured in Newtons (N)
23Net ForceNet force – the sum of the forces acting upon an object
24Balanced ForcesBalanced forces - occurs when the forces acting upon anobject are equal in size but opposite in direction
25Unbalanced ForcesUnbalanced forces – when unequal forces act on the sameobject; the object moves in the direction of the larger force
26Inertia and MassInertia - tendency of an object to resist any change in its motionThe greater the mass of an object, the greater its inertia.Think about playing ping pong with a bowling bowl…what’s the problem?Newton’s First Law of Motion (aka Law of Inertia)An object moving at a constant velocity keeps moving atthat velocity unless an unbalanced net force acts upon it.How does this apply to a car crash?Why can a seat belt prevent serious injury?