Forces # 35 Net force = 20 – 15 = 5 N (to the right) Net force = 10 – 0 = 10 N (upward) 20 N15 N 10 N

Forces # 36 The previous object will accelerate to the right and upward (both directions).

Forces # 37 Because the net force will tell you if the object’s motion is constant or how it is changing.

Forces # 38 The Newton (N) is the SI unit for force.

Forces # 39 Absolutely! Most 8 th graders miss this one! Examples A car going at a constant speed of 30 mph in a straight line Terminal velocity

Newton’s Laws # 40 Inertia – resistance to change in motion Weight – force due to gravity (w = m * g) Momentum – mass in motion

Newton’s Laws # 41 More mass = more inertia Less mass = less inertia

Newton’s Laws # 42 If an object has more inertia, you will need a larger force to change its motion.

Newton’s Laws # 43 It takes more force to get a bowling ball moving because the bowling ball has more inertia than a golf ball.

Newton’s Laws # 44-a First Law – Law of inertia Deals with balanced forces Objects want to keep doing what they are doing I.E. a car accident; water races, etc.

Newton’s Laws # 44-b 2 nd Law – F = ma Deals with unbalanced forces Relates the change in motion to the mass and force I.E. an object falling; pushing a cart, riding a bike/skateboard, etc.

Newton’s Laws # 44-c 3 rd Law – Forces act in pairs Deals with action / reaction forces Explains how objects are able to move I.E. swimming; walking, airplanes, rockets, etc.

Newton’s Laws # 45 F = m * a F = 25 * 5 F = 125 N

Newton’s Laws # 46 F = m * a 6 = m * 2 6 / 2 = m m = 3 kg

Newton’s Laws # 47 Force = same; mass is decreased Acceleration will increase.

Newton’s Laws # 48 Force = same; acceleration is decreased Mass will increase.

Newton’s Laws # 49 Momentum is NOT lost; the momentum before a collision = momentum after a collision.

Newton’s Laws # 50 More mass = more momentum More velocity = more momentum

Gravity # 51 Gravity – a force of attraction between 2 objects due to their masses and distance.

Gravity # 52 Law of Universal Gravitation – ALL objects in the universe attract each other.

Gravity # 53 Gravity exists EVERYWHERE.

Gravity # 54 Mass and distance affect gravity.

Gravity # 55 If mass increases, gravity increases! More mass = more gravity

Gravity # 56 If distance increases, gravity decreases. More distance = Less gravity

Gravity # 57 Mass is amount of matter that an object has Weight is a FORCE due to an object’s mass and gravitational acceleration. Mass does NOT change; weight changes once you leave earth.

Gravity # 58 You can never truly be weightless, because some object (star, planet, moon, etc.) will be exerting a force on you!

Gravity # 59 Mass is measured with a balance Weight (force) is measured with a scale

Gravity # 60 In the absence of air resistance, the softball and bowling ball will hit the ground at the same time. Gravity affects all objects equally (regardless of their mass) – this means that if you drop a feather and hammer, they hit the ground at the same time in the absence of air resistance!

Work and Machines # 61 Work – a force causes an object to move in the direction that the force is applied. Work is measured in Joules

Work and Machines # 62 For work to be done, you must apply a force to an object and the object must move in the direction that the force is applied.

Work and Machines # 63 a) Lifting an object (yes) b) Carrying a heavy object (no) c) Pushing a house (no) d) Holding 200 pounds over your head (no) e) Playing a sport (yes) f) Reading (n0) g) Pushing a cart down the hall (yes)

Work and Machines # 64 W = f * d W = 500 * 10 W = 5,000 J

Work and Machines # 65 Power – rate at which work is done Power is measured in watts

Work and Machines # 66 If a device is more powerful, then it does more work in the same amount of time.

Work and Machines # 67 If a device is more powerful, then it does the same amount of work in less time.

Work and Machines # 68 Why is a battery operated screwdriver more powerful than a hand operated screwdriver? a)Because it does more work more quickly b)Because it has a battery c)Because it has a motor d)Both B and C

Work and Machines # 69 P = w / t P = 50 / 10 P = 5 w

Work and Machines # 70 To do less work, you must either reduce the amount of force applied to the object or reduce the distance that the object travels.

Work and Machines # 71 To do more work, you must either increase the amount of force applied to the object or increase the distance that the object travels.

Work and Machines # 72 In a simple machine, if the input force is decreased, then the distance that this force is applied must be increased. This is know as the “force-distance trade-off.”