Forces

ForcesNewtons Second LawNewtons second law describes how force, mass, and acceleration are all connected!

An object accelerates when a force acts on its mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).Newtons Second LawF = M x A

Force = mass x accelerationNewtons Second LawMike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, can you compute how much force Mike is applying to the car?

Newtons Second LawA 0.06kg tennis ball is served with a racket. The racket applies a force of 330N to the ball and it leaves the racket with a speed of 100 km/hr. What was the tennis balls acceleration?

You push a skateboard with your hand. According to Newtons first law the skateboard should continue at a constant speed in the direction you pushed it forever unless acted on by another force.

In reality, what happens to the skateboard?Why?!

FrictionFriction the force that opposes motion between two surfaces that are touching each otherSurface materialAmount of force pressing the surfaces together

Types of FrictionStatic friction friction between two surfaces that are not moving past each otherSliding friction the force that opposes the motion of two surfaces sliding past each other.

Types of FrictionRolling friction less than static and sliding, due to friction between rolling object and surface it is rolling on

Air ResistanceAir resistance the opposing force on something that is falling due to gravity, friction of the air

Air ResistanceWhat is there is no air?!

Air ResistanceThe force of air resistance increases with speedWhen speed increases to the point that air resistance cancels the force of gravity you reach terminal velocity

Terminal Velocity forces on a falling object are balanced and the object no longer accelerates. The highest velocity a falling object can reach

Force = mass x accelerationHow much force is needed to accelerate a 66 kg skier at 2 m/sec2?

A 50 kg skater pushed by a friend accelerates 5 m/sec2. How much force did the friend apply?

A force of 20 N acts upon a 5 kg block. Calculate the acceleration of the object.

An object of mass 30 kg is falling in air and experiences a force due to air resistance of 50 newtons.Determine the net force acting on the object and calculate the acceleration of the object.

GravityAnything with mass is attracted by the force of gravity

Law of Gravitation any two masses exert an attractive force on each other

Gravity

GravityGravity is a basic forceNear Earths surface the acceleration due to gravity is 9.8m/s2F = m aForce due to Earths gravityF = m (9.8m/s2)

GravityIf you are sitting at your desk you are not acceleratingDoes this mean that gravity has disappeared?Of course not!Gravity constantly pulls on you, this is measured as weight

Weight gravitational force on an objectWeight = mass x 9.8m/s2

Weight vs. MassThe further apart two objects with mass are, the less gravitational pull there is between themThe further away from the surface of the Earth, the less you will weigh!

WeightA man stands on a scale and measures his weight. He then stands on the scale in an elevator. Will his weight be affect when the elevator travels upward? Will his weight be affected when the elevator travels down? If so, how will it be affected and when?

Projectile MotionIf you were to throw a ball will it continue in a straight line?

Objects down travel is straight lines, they tend to curve downGravity is pulling the object down to the Earth!

Projectile MotionAs you release a baseball you stop applying a force, its horizontal motion is constantWhen you let go, gravity takes over and begins to pull the ball down

Projectile MotionIf you throw a ball as hard as possible in a perfectly horizontal line, and drop a ball of the same mass from the same height, which would hit the ground first?Centripetal ForceRememberAcceleration is the rate of change of velocity due to a change in speed, direction or both

Centripetal Acceleration acceleration toward the center of a curved or circular path

Centripetal ForceWhat is required for an object to accelerate in any direction?A FORCE!!!F = M x A!Centripetal Force an unbalanced force acting on an object causing acceleration toward the center of a curved path

Newtons 3rd LawNewtons 3rd Law of Motion when one object exerts a force on a second object, the second object exerts a force on the first that is equal in size and opposite in direction

Every action has an equal and opposite reaction

Rocket Science!Newtons 3rd law even works in SPACE!Rocket engines work by forcing gases out of the back of the rocketThose gases exert an equal and opposite force on the rocket itself

MomentumMoving objects have a property called momentum

Momentum the product of mass and velocity; how much force is needed to change the motion of an object

Momentum = mass x velocityp= m x vMomentumOur units for momentum

kg m/s

Momentum has a direction because velocity has a direction!MomentumWhich of Newtons laws is momentum related to?

Newtons Second Law the law of inertia!

MomentumKnowing that momentum is related to Newtons 2nd law

Has your hand ever stung when you caught a ball?!A force is exerted on your hand as its momentum is changed

MomentumDoes anybody remember the formula for acceleration!?

How about the formula for force?!

MomentumMomentum A 1000kg car has stalled in the middle of the road. It must be pushed in order to get it out of the middle of traffic. Two men stop to help and push the car for 15s. The car reaches a speed of 4.5 m/s. With what force did they push the car?A force of 250 N is applied to an object that accelerates at a rate of 5 m/sec2. What is the mass of the object?

An object of mass 300 kg is observed to accelerate at the rate of 4 m/s2. Calculate the force required to produce this acceleration.

What is the momentum of a bird with a mass of 1kg and a velocity of 5m/s?

What is the mass of a bowling ball with a momentum of 25 kgm/s and a velocity of 5 m/s?

A 50 kg clown is launched from a cannon at 20 m/s. What is the recoil speed of the cannon if the cannon has a mass of 250 kg?

Conservation of MomentumMomentum of an object does not change unless its mass, velocity, or both change

Momentum can be transferred from one object to another

Newtons Laws!1st - An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Law of inertia!Newtons Laws2nd - Acceleration is produced when a force acts on a mass. The greater the mass the greater the amount of force needed.

F = m x aNewtons Laws3rd - For every action there is an equal and opposite re-action

when you push an object, it pushes back