Forces and Motion Part 2

Forces and Motion

Part 2

Objective 4: Describe the relationship between the mass of an object, the force applied to the object, and the object's acceleration.

Action and reaction forces are equal and act in opposite directions.

​Acceleration due to gravity is the same so a golf ball & a bowling ball object are both dropped from the same ledge will fall at the same rate; however, if they are pushed the golf ball will go faster because it has less mass.

Force is measured in Newtons, N.

Mass is measured in kilograms, kg.

Acceleration is measured in meters per second squared, m/s².

A car with a mass of 2400 kilograms is accelerating at a rate of 1.5 m/s² west. What is the net force acting on the car?

F = MAF = 2400 x 1.5 ... 3600N

A net force of 100 N east is acting on a bicycle, causing it to accelerate at a rate of 0.8 m/s² east. What is the mass of the bicycle?

M = F/A = 100/0.8 = 125 kg

When you push on a wall, the wall pushes back with a force equal in size and opposite in direction

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For every action there is an equal and opposite reaction

Multiple Choice

A swimmer reaches the end of the pool, turns around, and pushes off the wall with her feet. Which pair of action-reaction forces is exerted during the push?

• The force of gravity on the swimmer's body and the force of the wall on her feet.

• The force of the swimmer's feet on the wall and the force of the wall on her feet.

• The force of the swimmer's feet on the wall and the force of the water on her front.

• The force of gravity on the swimmer's body and the force of her feet on the wall.

Multiple Choice

If you push a bowling ball and a golf ball with equal force, what will happen?

• The acceleration of both balls will be equal and nonzero.

• The acceleration of the bowling ball will be greater than that of the golf ball.

• The acceleration of the golf ball will be greater than that of the bowling ball.

• The acceleration of both balls will be zero.

Multiple Choice

What will happen when the force on an object increases, assuming that its mass stays the same?

• Its mass will increase.

• Its acceleration will change.

• Its speed will decrease.

• There will be no effect.

Multiple Choice

A car has a mass of 2000 kilograms. The net force acting on the car is 5000 N toward east. What is the magnitude of the car's acceleration as a result of this force?

• 7000 m/s.

• 7000 m/s².

• 2.5 m/s².

• 2.5 m/s.

Multiple Choice

A force of 200 N toward north is exerted on an object with a mass of 40.0 kilograms. What is the acceleration?

• 5 m/s.

• 5 m.

• 5 m.

• 5 m/s² toward north.

When balanced forces act on an object, the object will likely not move and will remain at rest

These forces cancel eachother out

ex- parked car

Determine when forces are balanced or unbalanced on an object, and explain how this will affect the motion of the object.

• if an object at rest has forces acting upon it greater than zero, the objects motion will change; it may accelerate

• A change in velocity is an unbalanced force; ex: parachute opening on a race car helps bring it to a stop because a force opposite in direction and greater in magnitude applied to a moving object causes it to slow down

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An object in motion will remain in motion until it experiences an unbalanced force

Unbalanced Forces

When 2 unequal forces act in opposite directions, subtract the forces; when moving in the same direction, add the forces.

Pay attention to direction.

When unbalanced forces act on an object in the same direction, the object will likely stop ,pcing, change direction or start moving

Multiple Choice

Which statement BEST describes the forces acting on a parked car?

• There are no forces on the car.

• The car is being subjected to balanced forces

• The car is being subjected to unbalanced forces

Multiple Choice

One person pulls on a rope with a force of 400 N to the right. Another person pulls on the opposite end with a force of 600 N to the left. What is the net force?

• 400 N to the right

• 1000 N to the left

• 600 N to the left

• 200 N to the left

Multiple Choice

What happens when an unbalanced force is applied to an object at rest?

• it accelerates

• it moves up

• it remains at rest

• it gains mass

Multiple Choice

When two unequal forces act in opposite directions on a moving object, the object will

• absorb the forces.

• continue to move in the same direction.

• move in the same direction as the larger force.

• come to an immediate stop.

Multiple Choice

What happens when a force opposite in direction and greater in magnitude is applied to a moving object?

• The object will slow down.

• The object will always move backwards.

• The object will speed up.

• The object’s motion remains constant.

Multiple Choice

In a game of tug-of-war, you pull on the rope with a force of 100 N to the right and your friend pulls on the rope with a force of 100 N to the left. What is the net force on the rope?

• 100 N to the right

• 200 N to the left

• 0 N

• 200 N to the right

Describe the properties of electric and magnetic (electromagnetic) forces.

Electromagnetism is the forces and fields associated with charge

Magnets

• attract or repel other magnets

• affect or repel other magnets

• stronger charger and clser objects are make for greater attraction

• Ex- cobalt, nickel, iron

• NOT- aluminium, copper, silver, gold

​Positive and negative charges attract; same charges repel

​Bar Magnets- strongest at 2 ends; ends are called poles

Multiple Select

What is a property of a magnet?

• It attracts or repels other magnets.

• It attracts or repels any object with mass.

• It attracts or repels any metal.

• It affects electrically charged particles.

Multiple Choice

What happens to two charged objects as the distance between them increases?

• The force decreases.

• The force increases.

• The force is not dependent on distance.

• The force is unchanged.

Multiple Choice

Two electrically opposite charges are separated by a fixed distance. Which action will provide the greatest increase in the force of attraction between the charges?

• Double each charge and double the distance between the charges.

• Double each charge and halve the distance between the charges.

• Halve each charge and halve the distance between the charges.

• Halve each charge and double the distance between the charges.

Multiple Choice

One student rubs a balloon against his hair several times. Another student passes a comb through her hair several times. The students place the comb near the balloon and observe that the comb repels the balloon. Which is the most likely reason the comb is able to repel the balloon?

• The balloon and the comb have opposite electrical charges.

• The balloon has a negative charge and the comb is neutral.

• The balloon and the comb have the same electrical charge.

• The balloon has a positive charge and the comb is neutral.