Question

newtons first law of motion - 7.7d
unbalanced?
effect of forces
a car sits still
at a red light.
balanced
a car travels
at a constant
speed of 60
mph along a
straight
section of
highway.
unbalanced
a driver
switches
lanes to
prepare to
exit.
unbalanced
a driver steps
on the brakes
to avoid a
crash.
unbalanced

Explanation:

To solve the problem of determining the "Effect of Forces" for each scenario based on Newton's First Law of Motion (an object at rest or in uniform motion in a straight line will remain in that state unless acted upon by an unbalanced force), we analyze each case:

1. A car sits still at a red light

• Unbalanced?: Balanced (no net force, as the car is at rest).
• Effect of Forces: Since the forces are balanced, there is no change in motion (the car remains at rest).

2. A car travels at a constant speed of 60 mph along a straight section of highway

• Unbalanced?: The original answer here is incorrect. For an object moving at constant speed in a straight line, the net force is zero (balanced forces, because acceleration is zero). So the "Unbalanced?" column should be corrected to "Balanced".
• Effect of Forces: With balanced forces, the car continues moving at constant speed in a straight line (no change in motion).

3. A driver switches lanes to prepare to exit

• Unbalanced?: Unbalanced (changing lanes means changing direction, so acceleration occurs, requiring a net force).
• Effect of Forces: The unbalanced force causes the car to change direction (its motion changes).

4. A driver steps on the brakes to avoid a crash

• Unbalanced?: Unbalanced (braking causes deceleration, so a net force acts).
• Effect of Forces: The unbalanced force (braking) causes the car to slow down (its motion changes).

Filling in the "Effect of Forces" column:

Scenario	Unbalanced?	Effect of Forces
A car travels at a constant speed of 60 mph along a straight section of highway.	Balanced (corrected)	No change in motion (car continues at constant speed in a straight line).
A driver switches lanes to prepare to exit.	Unbalanced	Motion changes (direction changes).
A driver steps on the brakes to avoid a crash.	Unbalanced	Motion changes (speed decreases).

Key Principle (Newton’s First Law):

• Balanced forces (net force = 0) → No change in motion (object remains at rest or moves at constant velocity).
• Unbalanced forces (net force ≠ 0) → Motion changes (speed or direction changes).

Answer:

To solve the problem of determining the "Effect of Forces" for each scenario based on Newton's First Law of Motion (an object at rest or in uniform motion in a straight line will remain in that state unless acted upon by an unbalanced force), we analyze each case:

1. A car sits still at a red light

• Unbalanced?: Balanced (no net force, as the car is at rest).
• Effect of Forces: Since the forces are balanced, there is no change in motion (the car remains at rest).

2. A car travels at a constant speed of 60 mph along a straight section of highway

• Unbalanced?: The original answer here is incorrect. For an object moving at constant speed in a straight line, the net force is zero (balanced forces, because acceleration is zero). So the "Unbalanced?" column should be corrected to "Balanced".
• Effect of Forces: With balanced forces, the car continues moving at constant speed in a straight line (no change in motion).

3. A driver switches lanes to prepare to exit

• Unbalanced?: Unbalanced (changing lanes means changing direction, so acceleration occurs, requiring a net force).
• Effect of Forces: The unbalanced force causes the car to change direction (its motion changes).

4. A driver steps on the brakes to avoid a crash

• Unbalanced?: Unbalanced (braking causes deceleration, so a net force acts).
• Effect of Forces: The unbalanced force (braking) causes the car to slow down (its motion changes).

Filling in the "Effect of Forces" column:

Scenario	Unbalanced?	Effect of Forces
A car travels at a constant speed of 60 mph along a straight section of highway.	Balanced (corrected)	No change in motion (car continues at constant speed in a straight line).
A driver switches lanes to prepare to exit.	Unbalanced	Motion changes (direction changes).
A driver steps on the brakes to avoid a crash.	Unbalanced	Motion changes (speed decreases).

Key Principle (Newton’s First Law):

• Balanced forces (net force = 0) → No change in motion (object remains at rest or moves at constant velocity).
• Unbalanced forces (net force ≠ 0) → Motion changes (speed or direction changes).