Presentation on theme: "Equal forces in balance"— Presentation transcript:
1 Equal forces in balance Chapter 10 - ForcesQuestion – What causes an object to start moving, stop moving, or change directionAnswer - ForcesForce – a push or a pull30 lbs lbsEqual forces in balanceBalanced Forces
2 Equilibrium – when all forces acting on an object are in balance If all forces are in balance there is no acceleration. (The object is not moving or is at constant velocity100 lbsGround100 lbs
3 If the forces are not in balance there will be an acceleration Balanced ForcesThe force exerted by the motor in a forward direction is equal the force of friction in the opposite direction.Frictional force – a slowing force caused by objects or substances rubbing against each other.If the forces are not in balance there will be an acceleration50 mphFrom wind resistance, gears, etc..
4 NEWTON’S FIRST LAW OF MOTION An object at rest will stay at rest and an object that is moving will stay in motion unless acted on by an unbalanced forceAn object will tend to do what it is already doing.Inertia – the tendency of an object to resist changes in motion
5 NEWTON’S SECOND LAW OF MOTION Fnet = m(a) a = Fnet/mm/sec2(meter)kgNewtonNewton – the force required to accelerate a 1 kg mass 1 m/sec2Acceleration and force are directly proportional . If we double the force, we double the acceleration.Acceleration and mass are inversely proportional. If we double the mass, the acceleration is cut in half.
6 3 types of friction Sliding (when objects slide over each other) Rolling friction (less than sliding)Fluid – when objects move through a fluid such as water or air
7 Gravity – attraction between all objects that have mass The greater the mass the greater the gravitational attractionFree fall – acceleration due to gravity is m/sec2Air resistance – fluid friction of airThe higher the velocity, the greater the air resistance.Terminal velocity – when air resistance equals gravitational force
8 Skydiver terminal velocity 120 mph if body is horizontalOver 200 mph if body is vertical
9 Projectile Motion 9.8 m/sec2 9.8 m/sec2 or9.8 m/sec2They will strike the ground at the same time. Gravity accelerates them both at the same rate
10 Mass – measure of the amount of matter an object contains Weight – measure of gravitational pull measured in lbs on a spring scaleIs dependent on locationMass – measure of the amount of matter an object containsMeasured on a balance scale (with counter weights)Independent of location
11 NEWTON’S THIRD LAW OF MOTION If one object exerts a force on another object, then the second object exerts an equal force (but in the opposite direction) on the first object.These forces can be thought of as action and reaction forces.
12 Examples:RocketAction force – rocket pushing out gasesReaction force – gases pushing back against rocketGunAction force – powder and gun push against bulletReaction force – bullet pushes back against powder and gunCanoeAction force – paddle pushes against waterReaction force – water pushes back against paddle and canoe
13 Momentum Momentum = mass (velocity) The greater the momentum, the harder an object is to stop. Momentum can be increased by increasing velocity or mass.Which football player will be hardest to stop?Light and slowHeavy and slowLight and fastHeavy and fast
14 Law of conservation of momentum – the total momentum of any group of objects remains the same unless outside forces act on the objects. (friction is a force). This is used to analyze collisions.Examples:Before After1 kg 0 m/sec 2 kg m/sec1 kg 5m/sec 2 kg 0 m/secMomentum = 1 kg (5m/sec)Momentum = 5 kg(m) /secMomentum = 2 kg (2.5 m/sec)Momentum = 5 kg(m) /sec
15 In opposite directions Before Shotbullet and gunmomentum = 0After ShotGun BulletIn opposite directionsMomentum = 1 kg (10 m/sec)Momentum = 10 kg(m)/secMomentum = .01 kg (1000 m/sec)Momentum = 10 kg(m)/sec
16 Collision of bullet and clay Bullet ClayM = .01 kg (1000 m/sec) M = .99 kg (0m/sec)M = 10 kg(m)/sec M = 0After Collision Bullet in ClayMomentum = (.01 kg kg) (10 m/sec)Momentum = 10 kg(m)/sec
17 Satellites What keeps a satellite in orbit? Imagine you are standing on the top of a mountain and can throw a rock as fast as you want. Can you put the rock in orbit by throwing the rock straight out? How? Draw a diagram and explain the forces involved.If the velocity is perfect the drop of the rock due to gravity matches the curvature of the earth.