# Physics 2.2

### Physics 2.2

Speed and Velocity, Distance and Displacement:

    Speed is a scalar quantity.

Velocity is a vector quantity.

Distance is a scalar.

Displacement is a vector.

### 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

### Graphs you should know:

  Distance vs Time – Slope = ?

Velocity vs Time – Slope = ?

– Area = ?

### 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:

### 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?

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

Time 0 s 1 s 2 s 3 s 4 s Distance 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

### Statics:

  Forces which act on objects Combined concurrent forces are called the resultant force

### 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).

### Finding the Resultant Graphically:

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Parallelogram method: 1.

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Draw a mirror image of the two force vectors opposite them. Measure the resultant.

Triangle method: 1.

2.

Draw the second force vector from the head of the first.

Measure the resultant.

Parellelogram

### Equilibrium

  Static 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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### 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.

### More…

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Law of Inertia.

F = ma F 12 = F 21

### ???

1.

Which object has the most inertia?

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A 0.1 kg baseball travelling 20 meters/second.

A 10 kg sled at rest.

A 5 kg bowling ball traveling 3 meters/ second.

### ???

   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

### ???

 Which unit is equivalent to a newton per kg?

1. m/s² 2. W/m 3. j·s 4. kg·m/s

### 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: d y = v i t + ½at²

???

   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?

d x = v x t d y = v i t + ½at²

### A Projectile fired at an Angle:

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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.

### ???

 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

### Circular Motion

  Centripetal acceleration – a = v²/r Centripetal force – F = mv²/r

### ???

 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?

Newton’s Universal Law of Gravity

  F = Gm1m2/r² Weight = mg

### Friction

  Static friction: object is not moving – Fs = Us x Fn Kinetic friction: object is moving – Fk = Uk x Fn

### Impulse and momentum

  Impulse is the change in momentum.

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

– p = mv

### A Simple pendulum:

 Does mass effect the period?