Unit 1, Motion, Science Review

Newton’s 1st and 2nd Laws of MotionLaw of Motion

What it says What it means

First An object at rest will stay at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force.

If an object is moving, it will not move until a force acts on it. If you don’t pick up your dirty clothes from the floor, they won’t walk themselves into the clothes washer. They will remain on the floor until you pick them up and put them there yourself. If an object is moving, it will keep moving unless there is a force acting on it to change speed or direction. If we did not have gravity and you threw a ball, the ball would continue forever unless something else knocks it off of its path. Since we have gravity here on earth, and friction, the ball will be pulled to the ground by the gravity. The gravity and friction are what change the ball’s motion or trajectory.

Second Acceleration depends on the object’s mass and on the net force acting on the object. The relationship can be written as an equation.

Acceleration = Net Force/Mass

Acceleration is measured in m/s/s or Newtons.Mass is measured in kg

One way to increase acceleration is by changing the force or mass. If you were pulling your little brother in a wagon uphill, and you wanted to go faster, you could either pull harder or ask the brother to get out of the wagon : ). A decrease in mass causes an increase in acceleration, and increase in force has the same result.

Newton’s 3rd Law of MotionLaw of Motion What it says What it means

Third If one object exerts force on another object, then the second object exerts a force of equal strength in the opposite direction of the first object. .

For every action, there is an equal and opposite reaction. There are many , many examples of this concept. For example, when you jump, you push on the ground with your feet. This is an action force. You move upward because the ground is pushing you! When in a canoe, you would use paddles to push yourself forward in the water. When you push on the paddles, the water pushes back.

Two equal forces acting in the opposite direction on an object is considered to be balanced and there is no change in motion. If you and your friend push on a basketball in the air at the same angle, using the same amount of pressure, the ball will remain between the both of you between you hands.

Kinetic and Potential EnergyKinetic Energy Potential EnergyIn moving objects Stored energy that results from the

position of the object Increases as the mass increases- A bowling ball is more likely to knock down bowling pins than a golf ball is.

Has the ‘potential’ to do work.

Increases as the velocity (speed with direction) increases. The faster the ball, the more the kinetic energy.

The gravitational potential energy of an object is equal to the weight it takes to lift the object.

A pendulum’s kinetic energy is at 100% when it is at its lowest point

Elastic PE is the PE associated with objects that can be stretched. Think about when an archer pulls on his/her bow. The tighter the string, the greater the PE.

Kinetic Energy = ½ x mass x velocity²Think of the Ninja at Six Flags

Other Types of EnergyMechanical ThermalKinetic + Potential EnergiesMeasured in Joules (J)

Potential and kinetic energies of the particles in an object. Fast moving particles create heat.

Electrical ChemicalEnergy of electric charges Potential energy stored in bonds between

the atoms and molecules that hold chemical compounds together

Nuclear ElectromagneticPotential energy stored in the nucleus of an atom.

Travels in waves that have some electrical properties and some magnetic properties. Sunlight is a form of electromagnetic energy.

Energy TransformationMost forms of energy can be transformed into other forms

•A toaster transforms electrical energy into heat to toast bread, your body transforms chemical energy from food to mechanical energy to move your arms.

•If you were to juggle oranges, the orange at the highest point would have potential energy, and as gravity pulls it down, kinetic energy increases.

•Look at the energy transformation of a pendulum:

Law of Conservation of EnergyWhen one form of energy is transformed to another, no energy is destroyed in the process. The total amount of energy is the same before and after the transformation.

Graphing MotionYou can show the motion of an object on a line graph in which you plot distance v. time. Look at the following graphs. The first one shows a constant speed. The second shows acceleration, then no change in distance, then an increase of speed from 150m/min. at the beginning, to 200m/min. near the end.

Speed, Velocity and AccelerationSpeed Velocity Acceleration

The distance an object travels per unit of time

The distance an object travels per unit of time in a certain direction.

The rate at which velocity changes.

Measured in miles per hour (mph), meters per minute (mpm), kilometers per hour (kph)

Measured in miles per hour or km/h, or m/min., eastward or westward, or any other direction.

Formula:Average Speed = d/t

Same as speed Increasing speed, decreasing speed, or changing direction.

Simple Machines

6 Types• Levers• Screws• Wheel & Axel• Inclined Plane• Wedge• Pulleys

Lever• Rigid bar free to pivot or

rotate on a fixed point (fulcrum).

• Think of a see-saw.• Where would you put the

fulcrum to move the heavy rock easily?

fulcrum

Simple Machines –inclined planes and wedges

Inclined Plane• An inclined plane is a flat, sloped

surface. It can make moving heavy objects easier.

• It allows you to exert your input force over a longer distance. The input force needed is less than the output force. The output force is the force that you would need to lift the object without the inclined plane.

Wedge

• Thick at one end and tapered at the other

• Some examples of wedges are: a zipper, a knife, or an ax.

• Instead of moving objects along an inclined plane, you move the wedge.

Simple Machines – screws, wheel & axleScrew

• Inclined Plane wrapped around a cylinder. The spiral inclined plane forms the thread of the screw. Screws are used to fasten wood, and are also found on jar lids.

• As the threads of a screw turn, they exert an output force on the wood, pulling the screw into the wood. Friction between the screw and the wood holds the screw in place.

Wheel and Axle• Made of two circular or

cylindrical objects fastened together that rotate about a common axis.

Simple Machines Wheel & Axle, PulleyWheel & Axle Pulley• Made of two circular

objects fastened together that rotates about a common axis. A car’s steering wheel is another example of a wheel and axle.

•Made of a grooved wheel with a rope or cable wrapped around it. You use a pulley by pulling on one end of the rope, the output force pulls up on the object yu want to move. It makes work easier by decreasing the amount of input force needed, and by changing the direction of your input force, for example, you pull down on the flagpole rope, and the flag moves up.

•There are fixed and moveable pulleys.

Pulleys Continued

Think about it:If you need to push a box up an inclined plane coated with different surfaces where one section of the plane is sand paper, another is ice, and another is metal with tiny holes; which surface of the three would make the job easier for you?

What else would make the job easier for you? Why doesn’t the paper wad some of you throw behind my back, continue sailing on and on in the same position?

Think about it (more):Why doesn’t the paper wad some of you throw behind my back, continue sailing on and on in the same position?

If you have something on Earth that is too heavy to lift without a machine, why would you be able to lift it in

outer space?