MOTION

MOTION

• Motion – the act or process of an object changing position.

• How do we know when an object has moved?

• After we have observed it for a given time, and recorded its location.

MOTION

• 3 ways to measure (describe) motion– SPEED– VELOCITY– ACCELERATION

MOTION

• SPEED = Distance / Time

• Speed is a ratio– The relationship between how far

the object traveled, and the time it took.

• How far did it go in a given amount of time?

• How long would it take to go a given distance?

MOTION

• Since motion is rarely constant (uniform), we usually calculate average speed.

• Notice– We measure distance– We measure time– We calculate speed

http://www.youtube.com/watch?v=iRxs379Vq_k&feature=related

On any trip, there will be times when you will be going fast, and times when you will be going slow.

MOTION

• Speed = distance/ time = d/ t

• units = meters/ second = m/ s

• Practice Question• What is the average speed of a truck that makes a

120 km trip in 5 hours?

MOTION

• Velocity – refers to the speed and direction of a moving object. – Speed = 60 m/s– Velocity = 60 m/s West

– Velocity is a vector quantity (direction)– Speed is a scalar quantity (no direction)

MOTION

• Acceleration – refers to a change in velocity.– Change in speed or– Change in direction

• Change in direction is easy.

MOTION

• Acceleration – Change in speed

– = final velocity – initial velocity / time elapsed

– = end speed – beginning speed / time elapsed

– units = meters/second/second – = m/s2

or

Motion

• Acceleration = vf – vi

• Practice Question• An object speeds up from 5 m/s to 15 m/s in 2

seconds. What is the object’s acceleration?

t

MOTION

• Acceleration

• An object is travelling at 25 m/s. After 3 seconds the same object is travelling at 7 m/s. What is the object’s acceleration?

• Slow down is negative acceleration• Deceleration

MOTION

• Force is a push or pull that is capable of changing an object’s motion.

• A push or pull

• Measured in Newtons (N).

Motion

• Inertia – the tendency of an object to remain in unchanging motion.

• An object at rest will remain at rest, and an object in motion will remain in motion, until an unbalanced force acts on it.

Newton’s 1st Law of Motion

MOTION

• Friction always resists motion.– The force created by 2 things that are touching.

Friction will cause the object to slow down or come to a stop.

Bowling lanes are very smooth to limit friction.

MOTION

• Air Resistance– The friction that air particles have on moving

objects. It resists motion. – Also called Drag force.

MOTION

• Free fall – when air resistance is not a factor, 2 objects will fall at the same rate.

The bowling ball and the golf ball would hit the ground at the same time.

Air resistance would cause the feather to fall slowly.

MOTION• Newton’s 2nd Law of Motion

– The acceleration of an object is directly proportional to the net force acting on it, and inversely proportional to the mass of the object.

– An object will change its motion in the direction of the unbalanced force that acts on it. The amount of change depends on the amount of force and the mass of the object.

– Force = mass x acceleration ( F = m x a)

MOTION

• Forces in exactly the same direction are added.

10 N10 N10 N

10 N

OR

net force = 20 N net force = 20 N

MOTION

• Forces in exactly opposite directions are subtracted.

40 N10 N

net force = 30 N

50 N10 NOR

net force = 40 N

MOTION

• Forces that are equal and in exactly opposite directions will cancel out.

40 N40 N

net force = 0 N

50 N50 NOR

net force = 0 N

MOTION

• Forces that are not in exactly the same direction, or exactly opposite direction are more complicated.

• There is a formula to combine these vectors.

40 N

40 N

net force

MOTION

• Newton’s 2nd Law of Motion

• Practice Question• A rider and his bicycle have a combined mass of 75

Kg. How much force is required to cause them to accelerate 1 m/s2?

• An unbalanced force of 20 N causes an object to accelerate 5 m/s2. What is the mass of the object?

MOTION

• Momentum – the amount of force carried by a moving object.

• Force = mass x velocity F = m x v

Sports carMass = 1,200 KgVelocity = 90,000 m/s

Dump TruckMass = 7,500 KgVelocity = 900 m/s

What direction is the unbalanced momentum?

MOTION

• Newton’s 3rd Law of Motion• Whenever two objects interact, the force exerted on one object is equal

and in opposite direction to the force that acts on the other object.

MOTION

• Projectile motion– A combination of vertical and horizontal motion.

MOTION

• Centripetal force– The force that pulls an object out of its straight-

line path into a circular path. – ‘Center – seeking’

Why is it possible to swing a bucket of water in a circle, and not let any of the water spill out?

MOTION

• Gravity• The attractive force (pull) that exists between objects

in the universe.• Any 2 objects have gravity.• Related to the masses of the two objects and the

distance that separates them.

m1m2

distance

MOTION

• Gravity favors massive objects. • Like the pull that Earth exerts on us.

• Mass vs. Weight• Mass – the amount of matter in an object.• Never changes.• Weight – the force of gravity acting on an object.• Depends on gravity.

• Weight = mass x gravity constant (w = m x g)• Measured in Newtons• Gravity constant = 9.8 m/s2

ENERGY• Work – refers to the force applied to an object

and the distance that it travels. – Relationship / Ratio

• Work = force x distance (w = f x d)– Measured in Joules (J)

• Practice Question• A 15 Kg box is moved a distance of 20

meters. How much work is done?

ENERGY

• Work– Units = Joules (J)

• Joules is also the unit for energy– Work is related to the energy required to alter an

object’s motion?

ENERGY

• Power – the amount of work done in a given amount of time. – Relationship / Ratio

• Power = work / time ( P = w/t )– Measured in Watts (W)– The rate of energy use.

• Practice Question• An electric lift can raise a 90 kg box to a height of 15 m in 3

seconds. What is the power of the lift?

ENERGY

• Energy is the ability to do work.– Measured in Joules (J).

• 2 Categories of energy– Potential Energy – stored (not in use)– Kinetic Energy – energy in use (energy of motion)

ENERGY

• Potential energy due to location– Gravitational potential energy

• PE = mass x gravity constant x height • (PE = m x g x h)• Gravity constant = 9.8 m/s2

Whys is it easy to ski downhill?

Practice QuestionHow much potential energy is stored in a 100 Kg object that is raised to 8 m?

ENERGY

• Chemical potential energy– Stored in the bonds between atoms.

– When chemical bonds are broken it releases energy.– When chemical bonds are formed it requires energy.

ENERGY

• Kinetic energy– Energy that is in use.– Energy in motion.

• KE = ½ mass x velocity 2

• KE = ½ m x v 2

• Practice Question• How much kinetic energy is in a 0.28 Kg bullet that is

travelling at 40,000 m/s?

ENERGY

• Energy conversions– Potential vs. Kinetic

• 1. • 2. • 3. • 4. • 5.

Why does the pendulum eventually stop?

ENERGY

• Energy Forms– Chemical energy– Stored in the bonds between atoms in chemicals.

Food GasolineBatteries

ENERGY

• Energy Forms– Mechanical energy– Energy of moving parts– Energy of machines

Gears in a machine Wind turbine Sound

ENERGY

• Energy Forms– Radiant energy– Energy that travels through space

Light (Solar) Electromagnetic spectrum Heat (Infrared)

ENERGY

• Energy Forms– Electrical energy– The flow of electrical charge through a conductor.

Electricity Lightning

ENERGY

• Energy Forms– Nuclear energy– Energy from interactions between the protons and

neutrons in the nuclei of chemical atoms.

Nuclear power plantAtomic nucleus contains protons (+) and neutrons.