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Physics 2.2

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**Speed and Velocity, Distance and Displacement:**

Speed is a scalar quantity. Velocity is a vector quantity. Distance is a scalar. Displacement is a vector.

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Solve: A car begins to ride at 20 m/s north and finishes at 30 m/s north. What is the average velocity? Average velocity= initial + final velocity 2

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**Graphs you should know:**

Distance vs Time Slope = ? Velocity vs Time Area = ?

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Distance vs Time

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Velocity vs Time

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Velocity vs Time We can deduct interesting information from a velocity-time graph: The slope of the line is the acceleration, but the area under the line is the displacement! Let's see how to determine the displacement an object undergoes during a given time:

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**Free Fall: Use the Kinematic equations for constant acceleration.**

Use 0 m/s for initial and starting velocities, and g for acceleration (-9.81 m/s). After 1 second of free fall, what is the velocity of an object in free fall? 2 seconds?

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**Time, Distance, and Velocity of an Object in Free Fall:**

Top of Cliff 4.9 m 19.6 m 44.1 m 78.5 m Velocity v = 0 m/s v = 9.81 m/s v = 19.6 m/s v = 29.4 m/s v = 39.2 m/s

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**Statics: Forces which act on objects**

Combined concurrent forces are called the resultant force

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Question? Two concurrent forces on and object have a maximum resultant of 45 newtons and a minimum resultant of 5 newtons. What is the magnitude of each of these forces? Solution: find the resultants in the same and opposite directions. (20 N and 25 N).

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**Finding the Resultant Graphically:**

Parallelogram method: Draw a mirror image of the two force vectors opposite them. Measure the resultant. Triangle method: Draw the second force vector from the head of the first.

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Parellelogram

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Triangle-method

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**Equilibrium Static equilibrium: Dynamic equilibrium:**

An object at rest. Dynamic equilibrium: An object with the net forces acting on it are equal to zero. Ex/ an object in free fall that has reached terminal velocity.

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Free body diagram

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**Sir Isaac Newton’s Three Laws:**

An object in motion tends to stay in motion, unless acted upon by a force. When a force acts on an object, it will accelerate in the direction of that force When a force acts upon and object, that object will act with and equal and opposite force.

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More… Law of Inertia. F = ma F12 = F21

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**??? Which object has the most inertia?**

A 0.1 kg baseball travelling 20 meters/second. A 10 kg sled at rest. A 5 kg bowling ball traveling 3 meters/ second.

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??? An 8 N force is applied to a 4 kg block on a frictionless table. What is the magnitude of the block’s acceleration? F = ma 2 m/s²

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??? Which unit is equivalent to a newton per kg? m/s² W/m j·s kg·m/s

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**Projectile moving Horizontally:**

When an object is thrown from a height, there is both a horizontal and vertical component. Find time in the air with: dy = vit + ½at²

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??? A baseball is thrown horizontally at 25 m/s from a cliff 45 meters above the level ground. How far from the base of the cliff does the ball hit the ground? dx = vxt dy = vit + ½at²

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**A Projectile fired at an Angle:**

Set up two sets of data: Horizontal component x; Vertical component y; Use the kinematic equations to solve for both the horizontal and vertical components.

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??? A ball is thrown in the air at a 30˚ angle from the horizontal at a speed of 100 m/s. Find: Time in the air Max height range

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**Circular Motion Centripetal acceleration Centripetal force a = v²/r**

F = mv²/r

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??? A 2.0 E3 kg car travels at a constant speed of 12 m/s around a circular curve of radius 30. meters. What is the magnitude of the centripetal acceleration of the car as it goes around the curve? What direction is the centripetal force directed?

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**Newton’s Universal Law of Gravity**

F = Gm1m2/r² Weight = mg

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**Friction Static friction: object is not moving**

Fs = Us x Fn Kinetic friction: object is moving Fk = Uk x Fn

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**Impulse and momentum Impulse is the change in momentum.**

J = Ft = ∆p Momentum is mass x velocity. p = mv

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A Simple pendulum: Does mass effect the period?

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More pendulum stuff:

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