2 Forces Forces, Mass, and Acceleration the greater the force applied on an object, the greater the accelerationthe greater the mass of an object, the less acceleration
3 ForcesNewton’s Second Law of Motion – the net force acting on an object causes the object to accelerate in the direction of the net forceFormula for force:F = force m = mass a = acceleration F = ma
4 ForcesNewton’s Second Law of Motion – the net force acting on an object causes the object to accelerate in the direction of the net forceunits for force: NewtonsF = ma
5 Forces Sample Problems example: A person that weighs 70 kg jumps out of a plane at 9.8 m/s2. What is the force that gravity is exerting on the person?
6 Forces Sample Problems If gravity is exerting a force of 98 Newtons on an object in air, and the acceleration due to gravity is 9.8 m/s2, what is the object’s mass?
7 Forces Sample Problems If an object weighs 10 kg and has a force of 200 Newtons acting on it, what is the acceleration?
8 Forcesfriction – the force that opposes motion between two surfaces that are touching each otherNewton’s first law would say that if you push a skateboard, it would continue to move in a straight line at constant speed. We know however, that the skateboard slows down due to friction
9 Forces Types of Friction static friction – the friction between two surfaces that are not moving past each otherexample: when a box is so heavy you try and push it but it doesn’t moveNOT Moving
10 Forces Types of Friction sliding friction – the force that opposes the motion of two surfaces sliding past each otherexample: when you push a box it slides across the floor but the sliding friction makes it hard to push (but it DOES move)
11 Forces Types of Friction rolling friction – the friction between a rolling object (ex. tire) and the surface that it rolls onexample: a car’s tire rolling over the pavement or a train rolling on the railsusually much less friction than static or sliding friction
12 Forcesair resistance - a force that acts opposite to the motion of an objectexample: running against the wind or a parachute falling to the groundair resistance depends on the speed, size, and shape of the objectif no air resistance exists, two objects will fall at the same rate (even a feather and apple)
14 Gravitylaw of gravitation – states that any two masses exert an attractive force on each otherthe force of gravity increases when the mass of either object increasesthe force of gravity increases when the two objects move closer together
16 F = m x 9.8 m/s2 Gravity Gravitational Acceleration the gravitational attraction of Earth causes falling objects to have an acceleration of m/s2remember that F = ma so the force of gravity on an object near Earth’s surface is:F = m x 9.8 m/s2
17 Weight = mass x 9.8 m/s2 Gravity weight (W) – the gravitational force exerted on an objectmeasured in newtons (N)weight and mass are NOT the same because mass does not change based on location but your weight doesWeight = mass x 9.8 m/s2
18 Gravityexample: How much does a person with a mass of 70 kg weigh on Earth?on the moon, the acceleration due to gravity is only 1.6 m/s2 so you will weigh less on the moon
19 Gravity projectile motion the motion of anything tossed, thrown, shot, etc. will travel in a curved paththe object (projectile) will follow a curved path because of Earth’s gravitational pull
20 Forcescentripetal force – an unbalanced force that acts in the direction toward the center of motioncentripetal acceleration then, is the acceleration of an object toward the center of a curved or circular path
21 Forcescentripetal force – an unbalanced force that acts in the direction toward the center of motioncentripetal acceleration then, is the acceleration of an object toward the center of a curved or circular pathacceleration occurs during a curve because the direction is changing therefore making velocity changeexample: centripetal force (friction between the tires and road surface) causes a car on a curve to stay inward while the car’s inertia forces it outward
22 MotionNewton’s third law of motion – describes action-reaction pairs by stating that every action force has an equal and opposite reaction force.“for every action, there is an equal and opposite reaction”example: if an object hits water, water splashes back up
23 MotionA rocket works by igniting fuel which causes the gases to exert a downward force, resulting in air being pushed downward exerting a force upward, pushing the rocket up
24 Motion momentum = mass x velocity p = m x v momentum (p) - property that a moving object has that is related to how much force is needed to change its motionthe unit for momentum is kilogram meters per secondmomentum = mass x velocity p = m x v
25 momentum = mass x velocity Motionmomentum (p) - property that a moving object has that is related to how much force is needed to change its motiontwo trucks might have the same velocity but the bigger truck has more momentumexample: Compare the momentum of a 50-kg dolphin swimming at 10.4 m/s and a 6,300-kg elephant walking 0.11 m/s.momentum = mass x velocity
26 ForcesLaw of Conservation of MomentumIf no other force acts on bodies in motion, the momentum before collision is equal to momentum after collisionmomentum is not lost or created – it is conservedtotal momentum is zero.