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Transcript of Building Science Champions. Write a paragraph describing the picture. Words to include in your...
GRAVITY AND FRICTION Building Science Champions
IN THOUGHT
Write a paragraph describing the picture. Words to include in your paragraph:
Gravity Free fall Wind resistance Speed Acceleration Motion Velocity Terminal Velocity
OBJECTIVES
Describe friction and identify the factors that determine the friction force between two surfaces
Explain how mass differs from weight State the universal law of gravitation Describe the effects of gravity and air
resistance on an object in free fall
KEY TERMS
Force Contact force Noncontact force Net force Friction Fluid friction Rolling friction
Static friction Sliding friction Gravity Free fall Projectile Air resistance Terminal velocity
TYPES OF FORCE
Contact Force
Non-
conta
ct
Push Pull
Force – is a push or a pull Some forces are only applied when objects are in contact with one another; while others are applied when objects do not touchContact force is a push or pull on one
object by another that is touching it – someone playing a guitar
Noncontact force is a force that one object can apply to one another object without touching it – electric force
Are the following pictures contact or non-contact force
Using the force
STRENGTH OF FORCES
SI unit for force is the newton (N) Forces can be added together if they
are working in the same direction
Forces can be subtracted if they are working against one another
5 N
10 N
5 N10 N
10 N
5 N
10 N
10 N
What is the net force of the squares below?
15 N 15 N
5 N
0 N
NET FORCE AND DIRECTION OF FORCES The net force is the sum of all the
forces added together Vector analysis – is the analysis of the
different forces on an object resulting in the calculation of net force
Net force is given with a direction – in the example below 27 N right
17 N10 N
FRICTION
Surfaces may seem smooth but they have many irregularities
When two surfaces rub the irregularities of one surface get caught on those of the other surface
Friction – the force one surface exerts on another when the two rub against each other
Friction
NATURE OF FRICTION
The strength of the force of friction depends on two factors: the types of surfaces involved and how hard the surfaces push together.
Rough surfaces produce greater friction than smooth surfaces
Objects with greater mass and weight produce greater friction than lighter mass and weight
Friction releases energy in the form of heat
TYPES OF FRICTION
Fluid Friction – friction that occurs when an object moves through a fluid
Rolling Friction – friction that occurs when an object rolls over a surface
Sliding Friction – friction that occurs when an object slides over a surface.
Static Friction – prevents surface from sliding past one another
Sliding Friction
Fluid Friction
Static Friction – prevents you from sliding. If the box doesn’t move when force is applied it is because there is not enough force to overcome the static friction
GRAVITY
Gravity – is the force that pulls objects towards Earth
Gravity – is an attractive force that exists between all objects that have mass
Gravity is calculated on Earth as 9.8 m/s/s or 9.8 m/s2
FREE FALL
Free fall – when the only force acting on a falling object is gravity
Objects in free fall accelerate at a constant rate of speed – 9.8 m/s/s
1 sec – 9.8 m/s2 sec – 19.6 m/s3 sec – 29.4 m/s The mass of an object does not affect the rate of speed at Which the object falls
Flashphoto
PROJECTILE MOTION
Projectile – an object that is thrown or shot
An object that is dropped and one that is thrown horizontally are both in free fall
Horizontal motion does not interfere with free fall and both objects will hit the ground at the same timeBoth cannon balls will
hit the ground at the end of 6 seconds. B will travel a further distance.
Flash photo of a projectile
AIR RESISTANCE
Air resistance – a type of fluid friction that all objects encounter while falling through the air
Friction is the direction opposite to motion, so air resistance is an upward force
This why some objects fall faster than others Eventually air resistance will equal out the
force of gravity – when this happens the object is no longer increasing in velocity
Terminal velocity – the greatest velocity that an object reaches
WEIGHT
Weight – is the measure of force of gravity on an object, and mass is the amount of matter in that object
Weight = mass (kg) x acceleration due to gravity
Weight = mass x 9.8 m/s/s
UNIVERSAL GRAVITATION
The law of universal gravitation states: that the force of gravity acts between all objects in the universe
The moon has a gravitational effect on Earth, the Earth has a gravitational effect on the moon
Gravitational pull on objects compared to the gravity rate on Earth
GRAVITATIONAL FORCE & MASS
When the mass of one or both objects increases, the gravitational force between them also increases
F = G*m1*m2 / r2
F = ForceG = GravityM1 = Mass of first objectM2 = Mass of second objectr = Distance between the objects
1 kg
1 kg
2 kg
2 kg
Gravitational force increases if the mass of at least one objects increases.
GRAVITATIONAL FORCE & DISTANCE
The attraction between objects decreases as the distance between objects increases
Force
Distance
REVIEW
Weight and mass are not equal Weight = mass * gravity All objects have a gravitational
force/attraction to one another There are multiple types of friction
REFERENCES
Anderson, M. et all (2012) Physical Science. McGraw-Hill: Columbus
Frank, D.V et al (2001). Physical Science. Prentice Hall: New Jersey