Work Force Motion Energy Energy The ability to

Work, Force, Motion & Energy

Energy The ability to do work and cause change.

Law of Conservation of Energy cannot be created or destroyed Energy may change form, but the total amount remains the same

Kinds of Energy Potential – Energy at rest (stored energy) Kinetic – Energy of motion (moving energy)

Force A push or pull that could cause a change in an object’s motion

Balanced or Unbalanced Balanced forces = no change in motion – Often referred to as equilibrium Unbalanced forces = change in motion

Measuring Force can be measured using a spring scale Measured in newtons (N)

Force and Work Force can produce work if acted over a distance. Work can be calculated by w=Fxd Force can be calculated by F=w÷d

Gravity A force or attraction that exist between any two masses. – Gravity depends on the MASS of objects and DISTANCE between them – GREATER MASS or SMALLER DISTANCE = STRONGER GRAVITY

Mass The amount of matter in something – Measured in GRAMS or KILOGRAMS – Never changes. . . Remains constant

Weight FORCE that GRAVITY exerts (has) on a mass – Measured in newtons (N) – Changes depending on relationship between mass and gravity

Measuring Weight Example: You weigh 120 pounds on Earth – Gravity on the moon is 1/6 of that on Earth • Your WEIGHT on the moon = 1/6 of your weight on Earth (on moon you would weigh 20 pounds) • Your MASS on the moon = your mass on the Earth • What you are made of (mass) does not change… it remains constant

What is work? Work is done when a force causes an object to move in the same direction that the force is applied. The object must move.

Units of Measure Force is measured in Newtons (N) Distance is measured in meters (m) Work is measured in Joules (J) 1 J = 1 N/m

Is it work? A Joule is the amount of work done, BUT if work is to be done, then the object has to be moved in the same direction as the force. If you spent ½ hour pushing on a parked car, you were tired, hot and sweaty, you may feel like you have worked, but if the car never moved then you did NO work.

Example A force of 10 Newtons, that moves an object 3 meters, does 30 n-m of work. W = F x D (W = FD) W = 10 N x 3 m 30 N/m = 10 N x 3 m W = 30 Newton-meters A Newton-meter is the same thing as a joule

Work or No Work? Even though he is exerting force, nothing is being moved a distance, therefore no work is being done.

Work or No Work? Force is being exerted an object (fire truck) is being moved.

Motion The process of moving from one place to another 3 kinds: – Straight – Circular – Vibration (walking) (Bicycle Wheel) (Guitar String)

Sir Issac Newton & the Laws of Motion

Newton’s First Law of Motion 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 What does this mean?

What it means… There is a natural tendency of objects to keep on doing what they're doing. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

Example 1 What is the motion in this picture? What is the unbalanced force in this picture? What happened to the skater in this picture?

Example 2 This law is the same reason why you should always wear your seat belt.

Newton’s Second Law of Motion Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). What does this mean?

What it means… heavier objects require more force to move the same distance as lighter objects.

Newton’s Third Law of Motion For every action there is an equal and opposite reaction.

What it means whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

Example 2 The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.

Reminder: Work is… Work: remember that for work to be done the object must move in the same direction as the force. Work (W) = Force (F) x distance (d) W = Fd

Balanced or Unbalanced Forces