2 Frame of referenceA system of objects that are not moving with respect to one anotherTo describe motion accurately and completely, a frame of reference is necessary.
3 Relative MotionMovement in relation to a frame of reference.
4 Distance v. Displacement The length of the path between two pointsScalar quantitySI unit = meter (m)Ex. 100 metersDisplacementThe direction from the starting point and the length of a straight line from the starting point to the ending point.Vector QuantityEx. 100 meters East
5 Combining Displacements VectorA quantity that has magnitude and directionMagnitude can be size, length, or amountVectors are represented by arrowsLength of the arrow shows magnitudeThe way the arrow is pointing shows directionDisplacements are combined using vector additionVector addition is the combining of vector magnitudes and directions
6 Combining Displacements (cont.) Vectors that have the same direction are added together.Vectors that are in different directions are subtracted
7 Combining Displacements (cont.) When two or more displacement vectors have different directions, they are combined by graphing.
9 Combining Displacements (cont.) The vector in red is called the resultant vectorA resultant vector is the SUM of two or more vectorsThe resultant vector WILL ALWAYS point from the starting point to the ending point
10 Instantaneous v. Average Speed Average speed is for the entire time of the tripInstantaneous speed is the speed at a particular instantNOTE: both are scalar quantities!!!
11 SpeedAverage SpeedThe total distance traveled, d, divided by the time, t, it takes to travel that distanceSI unit is meter per second (m/s)
12 ProblemsWhile traveling on vacation, you measure the times and distances traveled. You travel 35 kilometers in 0.4 hour, followed by 53 kilometers in 0.6 hour. What is your average speed?
13 ProblemsA person jogs 4.0 kilometers in 32 minutes, then 2.0 kilometers in 22 minutes, and finally 1.0 kilometer in 16 minutes. What is the jogger’s average speed in kilometers per minute?
14 ProblemsA train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?
15 Speed (cont.) Instantaneous speed V, is the rate at which an object is moving at a given moment in timeSi unit is meter per second (m/s)
16 Graphing MotionTo graph speed, you place time (independent variable) on the x-axis, and distance (dependent variable) on the y-axisThese graphs are called distance v. time graphsThe slope on the graph equals the speedA positive slope shows positive directionA negative slope shows opposite directionA horizontal slope shows standing stillThe steeper the slope is, the higher the speed
17 Velocity Velocity is both speed and direction Therefore velocity is a?????Vector Quantity!A long vector shows a faster speedA short vector shows a slower speedVelocities are added using vector additionSI unit is meter per second (m/s)Average velocity = displacement/time ( Δx / t )Displacement = vector quantity from starting point to ending pointAre distance and displacement the same???
18 ProblemsA kayak is moving across a stream that is flowing downstream at a velocity of 4 km/h. The kayak’s velocity is 3 km/h. What is the magnitude of the kayak’s velocity relative to the river bank?
19 Acceleration Acceleration, a, is the rate at which velocity changes Acceleration = ANY CHANGE IN velocityMagnitudeDirectionIncrease in velocity = positive accelerationDecrease in velocity = negative accelerationSI derived unit is meters per second squared (m/s2)Acceleration is a vector quantity!Note: “change in” = delta (Δ)
20 Constant Acceleration Constant acceleration is a steady change in velocityEx. Taking off in an airplane or stopping at a red light. Both are constant acceleration.Which one is positive and which is negative?
21 Calculating Acceleration If change in velocity is positive than acceleration is positiveIf change in velocity is negative, than acceleration is negative
22 ProblemsAn airplane travels down a runway for 4.0 seconds with an acceleration of 9.0 m/s2. What is its change in velocity during this time?
23 ProblemsA car traveling at 10 m/s starts to decelerate steadily. It comes to a complete stop in 20 seconds. What is its acceleration?
24 ProblemsA ball rolls down a ramp, starting from rest. After 2 seconds, its velocity is 6 meters per second. What is the acceleration of the ball?
25 Graphing Acceleration Acceleration is graphed by putting time (independent variable) on the x axis, and velocity or speed (dependent variable) on the y axis.The slope of the graph is equal to the accelerationPositive slope = positive accelerationNegative slope = negative acceleration
26 Graphing Acceleration (cont.) Constant acceleration is represented by a straight line on a speed v. time graph.Constant acceleration is ALWAYS linear on a speed v. time graphConstant acceleration is represented by a curved line on a distance v. time graph
27 Instantaneous Acceleration Instantaneous acceleration is how fast a velocity is changing at a specific instantAcceleration is rarely constant, and motion is rarely in a straight line.Acceleration involves a change in velocity or direction or both, so the vector of acceleration can point in any direction.The vector’s length depends on how fast velocity is changing.For an object that is standing still, the acceleration vector is zero.
28 Force Force is a push or pull that acts on an object Forces cause: A resting object to moveA moving object to accelerate
29 Measuring Force A Unit of Force Newton (N) 1 kilogram to accelerate at a rate of 1 meter per second each second1 N = 1 kg·m/s2
30 Combining ForcesThe net force is the overall force acting on an object after all of the forces are combined.Same direction – addOpposite direction – subtractWhen the net force = zeroForces are balancedWhen the net force ≠ zeroForces are unbalancedForces add up to resultant force
31 FrictionFriction is a force that opposes the motion of objects that touchStatic frictionActs on objects that are at restActs in opposite direction of applied forceDynamic (sliding) FrictionActs on moving objects as they slide over a surfaceDynamic friction < static frictionCoefficient of FrictionThe ratio of the frictional force compared to the normal force (force due to gravity)μ = Ff/FN
32 Gravity Gravity is a force that acts between any two masses Attractive forceCauses objects to accelerate as they are pulled toward center of massTerminal velocity – force of air resistance = force of gravityCan act over large distances
33 Free FallFree fall is the movement of an object toward Earth due to the pull of gravityFor every second of fall time, the object’s velocity increases by 9.8 m/sTherefore, acceleration due to gravity, g, is 9.8m/s2t = 0 s v = 0 m/st = 1 s v = 9.8 m/st = 1 s v = 9.8 m/st = 1 s v = 9.8 m/s
34 ProblemsA child drops a ball from a bridge. The ball strikes the water under the bridge 2.0 seconds later. What is the velocity of the ball when it strikes the water?
35 ProblemsA boy throws a rock straight up into the air. It reaches the highest point of its flight after 2.5 seconds. How fast was the rock going when it left the boy’s hand?
36 Projectile MotionProjectile motion is the motion of a falling object (projectile) after it is given an initial forward velocityOnly two forces act on a projectileAir resistanceGravity
37 Famous Men In Physics Aristotle Galileo Newton Incorrectly proposed that a force is required to keep an object moving at a constant speedGalileoStudied how gravity produces constant acclelerationRolled balls down ramps yo!Concluded that moving objects not subject to friction or any other force would continue to move foreverNewtonFirst defined mass and forceIntroduced three laws of motion
38 Newton’s Laws of Motion First Law of MotionAn object in motion stays in motion and an object at rest stays at rest unless acted upon it by another objectInertia – the tendency of an object to resist a change in motionSecond Law of MotionThe acceleration of an object is directly proportional to the net force acting on it and the mass of the objectMass is a measure of the inertia of an objectΣF=ma; ΣF – net force, m – mass, a – accelerationThird Law of motionFor every action there is an opposite but equal reaction
39 ProblemsAn automobile with a mass of 1000 kilograms accelerates when the traffic light turns green. If the net force on the car is 4000 newtons, what is the car’s acceleration?
40 ProblemsA boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N?
41 ProblemsWhat is the upward acceleration of a helicopter with a mass of 5000 kg if a force of 10,000 N acts on it in an upward direction?
42 ProblemsAn automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s2 in the forward direction. What is the net force acting on the automobile? (Hint: Solve the acceleration formula for force.)
43 ProblemsA 25-N force accelerates a boy in a wheelchair at 0.5 m/s2. What is the mass of the boy and the wheelchair? (Hint: Solve Newton’s second law for mass.)
44 Weight and Mass Mass Weight Measure of inertia Amount of material an object containsWeightThe force of gravity on the mass of an objectWeight = mass times acceleration due to gravity
45 ProblemsIf an astronaut has a mass of 112 kilograms, what is his weight on Earth where the acceleration due to gravity is 9.8 m/s2?
46 Momentum Momentum is the product of an object’s mass and its velocity Objects with large momentums are harder to stop than those with smaller momentumsAll objects at rest have zero momentumMass is in kg; velocity is in m/sSI unit for momentum is kg∙m/s
47 ProblemsWhich has more momentum, a kilogram golf ball with a speed of 60.0 meters per second, or a 7.0-kilogram bowling ball with a speed of 6.0 meters per second?
48 Conservation of Momentum In a closed system, the loss of momentum of one object equals the gain in momentum of another object— momentum is conserved.A closed system means other objects and forces cannot enter or leave a systemObjects within a closed system can exert forces on one anotherAccording to the law of conservation of momentum, if no net force acts on a system, then the total momentum of the system does not change
49 Universal Forces There are four fundamental forces in the universe ElectromagneticStrong NuclearWeak NuclearGravitational
50 Electromagnetic Force Electric and magnetic force are two different aspects of the electromagnetic forceElectric force and magnetic force are the only forces that can both attract and repelOpposite charges attractLike charges repelElectromagnetic force is associated with charged particles
51 Nuclear Forces Strong Nuclear Force Weak Nuclear Force Holds a nucleus of an atom togetherStrong force that acts on the protons and neutronsWeak Nuclear ForceAn attractive force found in certain types of radioactive processesIs found inside protons and neutrons
52 Gravity Gravitational force acts between any two masses Force is dependant on mass and distanceForce decreases and distance between objects increasesThe weakest of the universal forces