1 Motion in Two Dimensions Using + or – signs is not always sufficient to fully describe motion in more than one dimension Using + or – signs is not always sufficient to fully describe motion in more than one dimension Vectors can be used to more fully describe motion Vectors can be used to more fully describe motion

2 Displacement The position of an object is described by its position vector, r The position of an object is described by its position vector, r The displacement of the object is defined as the change in its position The displacement of the object is defined as the change in its position Δr = r f - r i Δr = r f - r i

3 Velocity The average velocity is the ratio of the displacement to the time interval for the displacement The average velocity is the ratio of the displacement to the time interval for the displacement The instantaneous velocity is the limit of the average velocity as Δt approaches zero The instantaneous velocity is the limit of the average velocity as Δt approaches zero The direction of the instantaneous velocity is along a line that is tangent to the path of the particle and in the direction of motion The direction of the instantaneous velocity is along a line that is tangent to the path of the particle and in the direction of motion

4 Acceleration The average acceleration is defined as the rate at which the velocity changes The average acceleration is defined as the rate at which the velocity changes The instantaneous acceleration is the limit of the average acceleration as Δt approaches zero The instantaneous acceleration is the limit of the average acceleration as Δt approaches zero

5 Ways an Object Might Accelerate The magnitude of the velocity (the speed) can change The magnitude of the velocity (the speed) can change The direction of the velocity can change The direction of the velocity can change Even though the magnitude is constant Even though the magnitude is constant Both the magnitude and the direction can change Both the magnitude and the direction can change

6 Projectile Motion An object may move in both the x and y directions simultaneously An object may move in both the x and y directions simultaneously It moves in two dimensions It moves in two dimensions The form of two dimensional motion we will deal with is called projectile motion The form of two dimensional motion we will deal with is called projectile motion

7 Assumptions of Projectile Motion We may ignore air friction We may ignore air friction We may ignore the rotation of the earth We may ignore the rotation of the earth With these assumptions, an object in projectile motion will follow a parabolic path With these assumptions, an object in projectile motion will follow a parabolic path

8 Rules of Projectile Motion The x- and y-directions of motion can be treated independently The x- and y-directions of motion can be treated independently The x-direction is uniform motion The x-direction is uniform motion a x = 0 a x = 0 The y-direction is free fall The y-direction is free fall a y = -g a y = -g The initial velocity can be broken down into its x- and y-components The initial velocity can be broken down into its x- and y-components

9 Projectile Motion

10 Some Details About the Rules x-direction x-direction a x = 0 a x = 0 x = v xo t x = v xo t This is the only operative equation in the x- direction since there is uniform velocity in that direction This is the only operative equation in the x- direction since there is uniform velocity in that direction

14 More Details About the Rules y-direction y-direction free fall problem free fall problem a = -g a = -g take the positive direction as upward take the positive direction as upward uniformly accelerated motion, so the motion equations all hold uniformly accelerated motion, so the motion equations all hold

15 Velocity of the Projectile The velocity of the projectile at any point of its motion is the vector sum of its x and y components at that point The velocity of the projectile at any point of its motion is the vector sum of its x and y components at that point

16 Some Variations of Projectile Motion An object may be fired horizontally An object may be fired horizontally The initial velocity is all in the x-direction The initial velocity is all in the x-direction v o = v x and v y = 0 v o = v x and v y = 0 All the general rules of projectile motion apply All the general rules of projectile motion apply

26 Non-Symmetrical Projectile Motion Follow the general rules for projectile motion Follow the general rules for projectile motion Break the y-direction into parts Break the y-direction into parts up and down up and down symmetrical back to initial height and then the rest of the height symmetrical back to initial height and then the rest of the height