Distance and Displacement Motion Distance and Displacement

Frame of reference To describe motion you need to tell what direction an object is moving along with how fast the object is moving A frame of reference is a system of objects that are not moving with respect for one another For example, a butterfly flies by you, which frame of reference do you use, yourself or a plant

Motion Motion is simply a change in position Relative motion is movement in relation to a frame of reference Example when a train moves by a platform the people standing on the platform see the people on the train “moving by” but if the people on the train look at each other, they think they are “not moving”

Frame of reference Which frame of reference you choose depends on where you are For example, if you look out the train window a tree would be a good frame of reference for how fast the train is moving If you decide to walk on the train, looking at a seat will tell you how fast you are walking

Distance Distance is the length of a path between two points When an object moves, the distance is the length of the line from the starting point to the ending point The SI (System Internationale) for measuring distance is the meter (m) (around 3 feet) Most measurement made use kilometers or if the distance is smaller than a meter, then centimeters(cm) are used

Displacement Displacement provides how far away an object is and in what direction it is from a point It is the direction from the starting point along with the length of a straight line from the starting point to the ending point

Displacement cont. Example telling a person to walk 5 blocks is distance, but telling the person to walk 5 blocks north is displacement By giving the direction as well as the length you have given more accurate directions After a rollercoaster has completed a “ride” the displacement is zero

Two minute thought Explain to the person next to you how the displacement of the roller coaster is zero after the ride is finished Explain to the person next to you how you would measure the distance the roller coaster car traveled

Distance versus Displacement The roller coaster may travel a distance of 1 km but its displacement is zero since its starting point is the same as its ending point.

Vectors A vector is a quantity that has magnitude and direction Magnitude can be size, length or amount Vector addition is the combining of vector magnitude and directions Displacements can be added using vector addition

Vector Addition You can add two displacements represented by two vectors if they are in the same direction If the two displacements are in the opposite direction then they subtract from each other

Vector Addition 4km 2km Start finish 0 1k 2km 3km 4km 5km 6km Since the cars are moving in the same direction the displacements can be added using vector addition. 4km + 2km = 6km (displacement)

Vector Addition In this case the cars are moving in opposite direction so the displacements subtract from each other. 0 1km 2km 3km 4km Start Finish 4km – 2km = 2km (displacement)