2 force Define: Push or a pull Describe: a force is described by its direction in which it acts and its strengthStrength of force is measured in the Newton (N)Direction and strength can be represented by an arrowForce is in direction of the arrowIf you push a door you exert a force in a different direction than if you pull the door
3 Combining Forces- The Nature of Forcenet force = The combination of all forces acting on an objectIf you exert a force of 120 N on a desk and your friend exerts a force of 150 N in the same direction. What is the net force on the desk?
4 Unbalanced Forces- The Nature of ForceUnbalanced forces = result in a net force and cause motion.
5 Balanced Forces Balanced forces = do not cause motion. Net force = 0 - The Nature of ForceBalanced forces = do not cause motion.Net force = 0Balanced forces in opposite directions?How will that affect motion?
6 Questions A force is a push or pull. What is a force? - The Nature of ForceQuestionsQuestionAnswerA force is a push or pull.What is a force?What happens when forces combine?Forces combine to produce a net force.
8 FrictionA force that two surfaces exert on each other when they rub togetherActs in the opposite direction of the object’s motionDepends on 2 factors:1. how hard the surfaces push together2. Types of surfaces involved
9 friction Measured in Newtons Friction will eventually cause everything to stopRough surfaces = more friction
10 Important uses Walking Drive a car Slowing down – brakes Warm up your handsErase a mistakeYou could not walk without the friction between your shoes and the ground. As you try to step forward, you push your foot backward. Friction holds your shoe to the ground, allowing you to walk. Consider how difficult it is to walk on slippery ice, where there is little friction.
11 Problems with Friction Make movement difficult - Go to push a box across the floor or drag somethingFall off your bike and stop yourself by sliding on your kneesWastes energy: use extra fuelCreates heat (conservation of energy energy changes form – heat)Wears things out (moving parts, tires, shoes, use oil to reduce)
17 MassAmount of matter in an objectUnits for mass: kilograms
18 weight- Friction and GravityThe force of gravity on a person or object at the surface of a planet is known as weight.I have a revolutionary weight loss plan.A trip to the moon, where you would weigh 1/6 of what you do on EarthWhy wouldn’t this weight-loss plan have the effect most people want (the amount of matter or mass of a person’s body would not change)
19 1. What is the scientist’s mass? 2. What is exerting the greater gravitational force – Earth or the moon?3. Which is a more accurate measurement – mass or weight?What is the scientist’s mass?What is exerting the greater gravitation force
20 Free fall Only force acting on an object is gravity In free fall gravity is an unbalanced force causes the object to accelerate
21 Free fall Acceleration: change in directionAll objects regardless of their mass accelerate at the same rate.
22 Free Falling & velocity For every second a falling object’s velocity increases by 9.8 m/sVelocity: speed with a direction (down, SE, etc.)Start at 0 sec = 0 m/s1 sec = 9.8 m/s2 sec = 19.6 m/s3 sec = ?29.4 m/s
23 Air Resistance- Friction and GravityFalling objects with a greater surface area experience more air resistance.
24 Terminal velocityGreatest velocity that can be attained by an object in free fallAir resistance and velocity = balancedHumans = ~ 124 miles per hour
25 Comparing and Contrasting GravityFrictionPulls objects toward one anotherEffect on motionOpposes motionTypes of surfaces involved, how hard the surfaces push togetherDepends onMass and distanceMeasured inNewtonsNewtons