2 Vocabulary Acceleration Coefficient of Friction Equilibrium Force Free Body DiagramInertiaKinetic FrictionMassMotionNet ForceNewtonRolling FrictionStatic FrictionTerminal VelocityVector
3 Categories of Forces Contact – direct contact or touch between objects Long Range – acts at a distance
4 Types of Forces Pushing a crate across the floor – Applied Air Friction - DragOpposes motion – FrictionSupport force – NormalCreated in a rope, etc when connected to another mass – TensionForce due to gravity – WeightAre the forces above contact or long range?
5 Free Body DiagramsPictorial diagram of all the forces acting on an objectThe length of the arrow is proportional to the magnitude of the forceHow is the normal force drawn?How is weight drawn?
6 Free Body Diagram Practice Draw a FBD for the following:A flowerpot falls freely from a windowsill.A skydiver falls at a constant velocity.A cable pulls a box across a table. The box accelerates even though friction is present.A rope lifts a bucket.
7 Net Force The vector sum of all forces acting on an object Calculated for both the x and the yRepresented by ΣF
8 Net Force PracticePictorial diagram of all the forces acting on an objectThe length of the arrow is proportional to the magnitude of the force
9 1st Law of Motion Law of Inertia An object at rest will stay at rest, an object in motion will stay in motion unless acted upon by an unbalanced force greater than zeroEx. A car rider continues forward when the driver suddenly applies the brakes
10 2nd Law of Motion ∑F = ma W = mg Ff = µFn What is the net force? What is the unit for mass?Is mass the same quantity as weight?What is g?What is μ?On a flat surface, what is equal to the Fn ?
11 2nd Law PracticeIf all of the forces acting on an object balance so that the net force is zero, thenA. The object must be at restB. The object must be at a constant velocityC. The object may be at rest or at a constantvelocity
12 2nd Law PracticeTwo astronauts tug on opposite sides of a satellite. The first astronaut tugs to the left with a force of 30 N. With what force does the second astronaut tug in order to keep the satellite moving toward him at a constant velocity of 20 m/s?A. 30 NB. – 30 NC. 0 ND. 50 NE. 1.5 N
13 2nd Law PracticeThe maximum (or terminal) velocity of a skydiver (m=70kg) with arms and legs extended is about 120 mi/h (= 53.6 m/s). What force does air resistance exert on the skydiver?A. 0 NB. 13 NC. 70 ND. 700 NE N
14 2nd Law PracticeAn airplane has a mass of 3.1 x 104 kg and takes off under the influence of a constant net force of 3.7 x 104 N. What is the acceleration that acts on the plane?
15 2nd Law Practice Weight and mass are A. always the same B. inversely proportionalC. based on locationD. none of the above
16 2nd Law PracticeA large (150 kg) refrigerator needs to be moved across the kitchen. Fred pulls with a force of 100 N and Wilma pulls with 75 N in the same direction. If the force of friction was 40 N, what will be the acceleration of the refrigerator?A 1.17 m/s2B 0.90 m/s2C 0.43 m/s2D 135 m/s2
17 2nd Law PracticeWhen a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal velocity. This means thata. the acceleration is equal to g.b. the force of air resistance is equal to zero.c. the effect of gravity has died down.d. the effect of gravity increases as he becomes closer to the ground.e. the force of air resistance is equal to the weight of the parachutist.
18 2nd Law PracticeThe force of kinetic friction is always __________ than the force of static friction.a. less thanb. equal toc. greater thand. varies depending on situation
19 2nd Law PracticeThe normal force acts ______________ to the surface of the contact objecta. perpendicularb. parallelc. at an angle
20 3rd Law of MotionFor every action, there is an equal and opposite reaction
21 3rd Law PracticeA mass is suspended on a spring. The reaction force to the force of the gravity from the Earth acting on the mass is the force exerted by theA. mass on the EarthB. mass on the springC. spring on the massD. spring on the EarthE. Earth on the mass