Force and Motion

Work In order to have work, force and motion must be acting in the same direction. Non-example of work—holding a backpack. Carrying a box

Inertia The tendency of an object to resist change in motion. Ex. A ball on the floor wants to remain still. A person on a bike wants to continue at the same speed.

Influences on Inertia Mass-the greater the mass of an object, the greater its inertia Ex.-a ton truck will take more force to move than a Volkswagen Bug; it will also take more force to stop.

Forces affecting inertia Friction-the force acting between two objects in contact. Friction opposes movement. Friction is what slows things down (brakes on a vehicle, a ball that stops rolling).

Gravity Gravity-the force that pulls all objects toward the earth. Newton was the first to come up with the concept of gravity.

Sir Isaac Newton

Speed Speed is the distance traveled divided by the time needed to travel the distance The SI Unit for speed is meters/second For example: 5 meters/second

Velocity The speed and direction an object is moving. 55 mph north is an example

Acceleration A change in speed or direction. Ex. A vehicle going 35 mph stops. A vehicle going 35 mph north goes around a curve and begins going east.

Mass Mass is the amount of matter in an object. Please remember that this is not the weight of an object. Weight is when gravity pulls down on an object, mass is the amount of matter in an object

Question about Mass If a person weighs 100 pounds on earth, will their mass change on a planet with two times the gravitational pull? If a person weighs 100 pounds on earth, will their weight change on a planet with two times the gravitational pull?

Buoyancy Buoyancy occurs because an object is being pushed up by a liquid.

Density An object that is more dense will sink. An object that is less dense will float. You can change the density of an object by changing its shape.

Relative Motion The position of an object is described relative to another object, which is the reference point. If an object is beside the tree and later is farther away from the tree, the object has moved relative to the other object.

Displacement The distance and direction between starting and ending positions. By following a hiking trail the total distance you travel is 22 km. However, you end up only 12 km northeast of where you started.

Newton’s 1st Law An object at rest (or in motion) will remain at rest (or in motion) unless acted on by a force (push or pull) Ex.-If a person is in a car traveling 65 mph, and the car stops suddenly, the person will continue to travel 65 mph.

Newton’s 2nd Law Force=mass x acceleration Balanced forces result in no movement. Unbalanced forces result in movement in the direction of the force.

Net Force

Newton’s 3rd Law For every action force there is an equal and opposite reaction force. Ex-you push down on your chair with the same force your chair pushes up on you with.

Newton’s Cradle Which of Newton’s Laws does a Newton’s cradle show? All of them!!!

Action vs. Reaction Action Force—when something is pushed upon (me pushing on the door). Reaction Force—when that thing pushes back (the door pushes back on me).

Graphing Distance/Time Look at the following slides to determine speed and acceleration. If the line is straight, the speed and is constant (1m/s) If the line is curved, the object has accelerated.

In the 2nd graph, how long did it take him/her to go 1m? 2m? In which one second did he/she cover the most distance?