Forces & Motion Review

What is Energy? Kinetic Energy– objects in motion based on mass and speed Potential Energy—objects have stored energy because of position based on weight and height from the ground

Describe Motion

Motion When an object changes its position, motion has occurred. Distance- How far an object has moved. Displacement- How far an object has moved in relation to its starting point. Example: Two runners travel along the same straight path in a straight line for 500 meters. At the end of the run their distances are the same but their displacements are different. How can this be so?

Displacement vs. distance a. Distance – how far something moves(entire Pathway) b. Displacement – the distance and direction of an object’s change in position from its starting point

The hydrant– the hydrant is what the dog’s motion is being judged by. Review Question A dog is running past a fire hydrant, relative the hydrant the dog is traveling at 5m/s. What is the reference point? The hydrant– the hydrant is what the dog’s motion is being judged by. If a butterfly moves from one flower to another that is 5 meters away, but returns to the original flower? What is the distance the butterfly traveled? What is the displacement of the butterfly? 10m 0m

Describe Speed

Describe Speed A way to describe motion Average speed - Rate of motion calculated by dividing the distance traveled by the amount of time it takes to travel that distance Constant speed - Speed that does not change Instantaneous speed - Speed of an object at any given time

What is the formula used to calculate speed?

What is the formula for calculating speed? Speed is calculated by dividing distance by time –

Calculate This Speed A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?

Remember to include the UNITS!! Calculate this Speed: A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running? Speed = Distance ÷ Time Speed = 100 m ÷ 20 s Speed = 5m/s Remember to include the UNITS!!

Distinguish Between Speed & Velocity

Distinguish Between Speed and Velocity Speed describes distance and time Velocity describes distance, time, and direction Velocity uses displacement instead of distance when calculating Average Velocity

Review Question A ball is kicked west 150 meters in 15 seconds. What is the balls velocity? V= d/t V= 150/15 V= 10m/s west If a boy is walking west at 3m/s on a train going east at 60m/s? What is the boys resultant velocity? V= 60m/s E – 3m/sW V= 57m/s East

Interpret The Graph Below:

Interpret The Graph Below: The graph shows an object which is not moving (at rest). The distance stays the same as time goes by because it is not moving.

Interpret The Graph Below:

Interpret The Graph Below: The graph shows that the objects distance increases as time passes. The object is moving and so it has velocity. The straight line shows it is a constant (not changing).

Interpret The Graph Below:

Interpret The Graph Below: Just like the previous graph, this graph shows an object moving with constant velocity

Interpret The Graph Below:

Interpret The Graph Below: The curve in the graph shows that the objects velocity is changing as time passes. This is acceleration.

Interpret The Graph Below:

Interpret The Graph Below: In the first part of the graph the object is moving with constant velocity. In the second part of the graph the object is at rest (not moving). In the third part the object is again moving with constant velocity.

Analyze the Graph Instantaneous Speed .2km/min 6km 6km What does each dot on the graph Represent? What are the changes in Motion? What is the average Speed of this Object? What is the Distance Traveled? What is the Displacement? Instantaneous Speed Constant speed then an increase in speed at aConstant rate, then stopped then a constant speed again .2km/min 6km 6km

Describe Acceleration

Describe Acceleration A change in velocity – which may be: A change in speed Starting Stopping Speeding up Slowing down A change in direction Acceleration is caused by unbalanced forces More

Describe Acceleration Deceleration is also called negative acceleration - it means an object is slowing down When acceleration is calculated, it may be a negative number

Review Question A child is riding in a circle at a constant speed. Is the child accelerating? Yes, because of a change in direction. Is a car slowing to a stop, acceleration? Yes, because a change in speed is acceleration A baseball is traveling across the field at 30m/s and then slows to a speed of 10m/s in 5seconds. What is the balls acceleration? Vf- Vs = 10m/s – 30m/s = --20m/s= --4m/s/s t 5s 5s

Interpret The Graph Below:

Interpret The Graph Below: The graph shows that the objects velocity does not change as time passes. It shows constant velocity.

Interpret The Graph Below:

Interpret The Graph Below: The graph shows that the objects velocity is increasing as time passes – it is accelerating. The straight line shows that it is constant acceleration.

Which line had a constant speed or no acceleration? Which Line shows deceleration? Which line shows faster acceleration B or D? C A B --steeper Slope than D

Explain Forces

Explain Forces When all the forces acting on an object equal each other : they are balanced Balanced forces do not cause a change in motion When one force is greater than another it forms unbalanced forces. Unbalanced forces equal movement in the direction of the greatest force

How Can Forces Affect Objects? Slow them down Speed them up Stop them Start them Change their direction Change their shape

Types of Forces Gravity: pulling force exerted on all objects Friction: pushing force that opposes motion Caused by the contact of small ridges and valleys between objects

Review Question A mouse pulls with a force of 10 N on a piece of cheese that weighs 5N. What is the net force? Is there movement? Yes, because the net force is 5N in the direction the mouse pulled. A furniture mover exerts 100N of force on a piano that weighs 100N. What is the net force? Is there movement? NO, because the net force = zero. No movement. The furniture mover’s force must exceed 100N. 3. Is sitting in a chair an example of balanced or unbalanced forces? Balanced

Describe Friction

Describe Friction Force that resists motion between two touching surfaces Acts in the opposite direction of the object’s motion Produces heat

Describe Friction 2 Types: Kinetic: occurs when moving objects are in contact Static: occurs when objects are in contact but not moving Sliding Friction takes more force to oppose than Rolling Friction

Describe Friction Helpful : friction helps us walk, brake and stop and hold things without dropping them Harmful: friction can wear out parts on a machine, wear holes in socks, and prevent you from sliding down a slide Increase friction by: increasing force pressing objects in contact or increase the roughness of the surface of the objects in contact Decrease friction by: smoothing the surface Using lubricants: water, oil, wax etc

Indicate if the friction is helpful or harmful Soil erosion--- Review Question Indicate if the friction is helpful or harmful Soil erosion--- Car tires’ tread wearing down Brakes stopping your bike Walking without slipping Rubbing your hands to warm them a hole developing in your sock Increasing Friction or Decreasing Friction Using a cooking spray in the pan before cooking eggs Pushing harder on the eraser to remove stray marks on a wall Using a tissue with lotion on a runny nose Wearing batting gloves Waxing skies before using them harmful harmful Helpful Helpful Helpful harmful decrease Increase decrease Increase decrease