Speed The distance an object travels per unit time. We use metric (SI) units and it is meters per second (m/s) Usually the speed of an object changes as it moves from one place to another
Instantaneous Speed The speed of an object at a single point in time Speedometer
Average Speed The total distance traveled divided by the total travel time ___ V = d/t ____ V = average speed d=distance t=time
Practice Problems What is the average speed of a car that travels a distance of 750m in 25s ? What is the average speed of a motorcycle that travels a distance of 300m in 10s ? What is the average speed of an airplane traveling a distance of 1000m in 10s ?
Velocity The speed of an object and the direction of the motion Objects have different velocities if they are moving in different directions or a different speeds
Acceleration Section 3-2 Acceleration is the change in velocity divided by the time it takes that change to occur Acceleration
ChangingChanging Direction A change in velocity can be either a change in how fast something is moving or a change in the direction of the movement
Calculating Acceleration When an object moves from one place to another, it might speed up, slow down, and change directions many times. Each change in velocity causes the acceleration of the object to change
Balanced Forces Force does not always change velocity, two or more equal forces acting on an object in opposite directions can cancel each other out. The net force is zero.
Unbalanced Forces Unequal forces applied in opposite directions lead to a net force in the direction of the larger force and movement in that direction
Friction The force that opposes the sliding motion of two surfaces that are in contact
What Causes Friction? Frictional force depends on the materials that the surfaces are made of and the roughness of the two surfaces All surfaces have bumps and dips in them that can cause contact and thereby friction (microwelds)
Frictional Force FF increases when the force pushing the surfaces together increases.
Static Friction The frictional force that prevents two surfaces in contact from sliding past each other. Once the applied force is greater, the object will move.
Rolling Friction Rolling friction is usually much less that static friction, that is why we use wheels!
Air Resistance This force opposes the motion of objects that move through the air. Air resistance acts in the opposite direction of the objects movement The greater the surface area of the object the greater the power of air resistance on that object
Terminal Velocity As an object falls it accelerates due to gravity, however air resistance eventually steps in to slow the object to a speed that no longer increases…that equaled out speed is called terminal velocity!