The forces Law and freefall

F m x a Newton’s Second Law Acceleration of an object is directly proportional to the resultant force exerted on it and inversely proportional to its mass. The harder you push something the faster it will speed up.

x F force = mass x acceleration Resultant force is measured in newtons (N). Mass is measured in kilograms (kg). Acceleration is measured in metres per second per second (m/s2). F x

How do we use Newton’s second law? A car has a mass of 1 000 kg. What force must the car’s engine supply to cause an acceleration of 2 m/s2? force = mass x acceleration Photo credit: Piotr Gilko = 1 000 x 2 = 2 000 N

How do we use Newton’s second law? A lorry has a mass of 12 000 kg. What acceleration is caused by a force of 10 000 N? force = mass x acceleration force mass acceleration = = 10 000 12 000 Photo credit: Jelle Weidema = 0.83 m/s2

A B C normal sea water Dead Sea sea water fresh water 1. In which kind of water is the upthrust greatest? 2. When the boat in diagram B has several people in it, it looks more like the boat in diagram C. Explain why this is so.

15 £1 Million 14 £500,000 If the driving force and the air resistance force exerted on an aircraft in flight are balanced…. 13 £250,000 12 £125,000 11 £64,000 10 £32,000 9 £16,000 8 £8,000 7 £4,000 6 £2,000 5 £1,000 4 £500 3 £300 2 £200 50:50 1 £100 B: The aircraft will fly at constant height A: The aircraft will stop C: The aircraft will reverse D: The aircraft will fly at constant velocity

Which of the following is not a result of friction? 15 £1 Million 14 £500,000 13 £250,000 12 £125,000 Which of the following is not a result of friction? 11 £64,000 10 £32,000 9 £16,000 8 £8,000 7 £4,000 6 £2,000 5 £1,000 4 £500 3 £300 2 £200 50:50 1 £100 B: increase in temperature A: deceleration D: acceleration C: wearing away surface

Objective: To learn the difference between mass and weight.

Mass and Weight Mass (kg) Weight on the Moon (N) Weight on Earth (N) Weight on Jupiter (N) 1 1.6 10 26 4 6.4 40 104 6 9.6 60 156 2 3.2 20 52 0.5 0.8 5 13 3.8 6.08 38 98.8 a b c d e f

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there.

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there. F Living on Jupiter would make you gain weight.

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there. F Living on Jupiter would make you gain weight. T The weight of an average apple is 1 kilogram.

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there. F Living on Jupiter would make you gain weight. T The weight of an average apple is 1 kilogram. F 1 Newton of steel weighs more than 1 Newton of feathers.

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there. F Living on Jupiter would make you gain weight. T The weight of an average apple is 1 kilogram. F 1 Newton of steel weighs more than 1 Newton of feathers. F Your weight on the Moon is different than your weight on Jupiter.

TRUE or FALSE Astronauts on the Moon feel lighter because there is no gravity there. F Living on Jupiter would make you gain weight. T The weight of an average apple is 1 kilogram. F 1 Newton of steel weighs more than 1 Newton of feathers. F Your weight on the Moon is different than your weight on Jupiter. T

An apple and a feather falling in a vacuum container

Falling objects Objective: Why do heavy and light things fall down at the same speed?

To describe the velocity – time graph of a skydiver. Terminal Velocity air resistance / drag ?? Objective: To describe the velocity – time graph of a skydiver. gravity / weight ??

Air resistance Weight The skydiver has just jumped out of the plane

Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance

E F Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance B to C: Sky diver is facing air resistance equal to the downward force of weight. constant velocity (terminal velocity).

E F Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance B to C: Sky diver is facing air resistance equal to the downward force of weight. constant velocity (terminal velocity). Point C: Parachute has opened.

E F Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance B to C: Sky diver is facing air resistance equal to the downward force of weight. constant velocity (terminal velocity). Point C: Parachute has opened. C to D: sky diver is slowing down, parachute caused air resistance to increase (decelerating). Air resistance > Weight

F Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance B to C: Sky diver is facing air resistance equal to the downward force of weight. constant terminal velocity. Air resistance = Weight Point C: Parachute has opened. C to D: sky diver is slowing down, parachute caused air resistance to increase (decelerating). Air resistance > Weight D to E: Due to the slowing down, air resistance has reduced, so the sky diver is moving at a constant low velocity. Air resistance = Weight

Air resistance Weight A to B: Sky diver is gaining speed (accelerating). Weight > Air resistance B to C: Sky diver is facing air resistance equal to the downward force of weight. constant terminal velocity. Air resistance = Weight Point C: Parachute has opened. C to D: sky diver is slowing down, parachute caused air resistance to increase (decelerating). Air resistance > Weight D to E: Due to the slowing down, air resistance has reduced, so the sky diver is moving at a constant low velocity. Air resistance = Weight Point F: Sky diver hits ground.