3. identify the forces
situation balanced or unbalanced? explain (use sentence stem)
a book resting on a desk
the forces are because the book is
a ball rolling and slowing down
the forces are because friction is
a person pushing a box and it starts moving
the forces are because the push
a car moving at the same speed in a straight line
the forces are because the car
4. apply what you know
1. if you slide a toy car across the floor, it eventually stops because of:
a) inertia b) gravity c) friction d) air
2. when balanced forces act on an object, the object will:
a) speed up b) slow down c) not change motion d) spin
3. when unbalanced forces act on an object, it will:
a) stay still b) change motion c) float d) disappear
5. think and explain
1. newtons first law means that.
2. a real - life example of inertia is.
3. when forces are balanced,.
4. when forces are unbalanced,.

Question

Accepted Answer

# 3. Identify the Forces
## A book resting on a desk
### Brief Explanations:
When a book is resting on a desk, it is in a state of equilibrium. The force of gravity pulling the book downwards is balanced by the normal force exerted by the desk upwards. Since there is no net force acting on the book (it is not accelerating), the forces are balanced.
### Answer:
Balanced; balanced; not accelerating

## A ball rolling and slowing down
### Brief Explanations:
As the ball rolls, friction acts in the opposite direction of its motion. This frictional force is an unbalanced force because it causes a change in the ball's velocity (it slows down). According to Newton's second law ($F = ma$), an unbalanced force ($F
eq0$) leads to acceleration ($a
eq0$). Here, the acceleration is negative (deceleration) due to the frictional force.
### Answer:
Unbalanced; unbalanced; acting against the ball's motion

## A person pushing a box and it starts moving
### Brief Explanations:
Initially, when the box is at rest, the frictional force (static friction) opposes the applied force (the push). Once the applied force exceeds the maximum static - friction force, the box starts to move. At the moment it starts moving, there is a net force in the direction of the push. Since there is a net force ($F_{net}=F_{push}-F_{friction}>0$), the forces are unbalanced.
### Answer:
Unbalanced; unbalanced; greater than the friction force

## A car moving at the same speed in a straight line
### Brief Explanations:
When a car is moving at a constant speed in a straight line, the force provided by the engine (thrust) is balanced by the resistive forces (such as air resistance and friction). According to Newton's first law ($F = ma$, when $a = 0$ (constant velocity), $F_{net}=0$). So, the forces acting on the car are balanced.
### Answer:
Balanced; balanced; moving at a constant velocity

# 4. Apply What You Know
## 1. If you slide a toy car across the floor, it eventually stops because of:
### Brief Explanations:
- Inertia ($a$) is the tendency of an object to resist changes in its state of motion. It does not cause the car to stop.
- Gravity ($b$) acts vertically. While it affects the normal force (and thus friction indirectly), it is not the direct cause of the car stopping as the car's motion is horizontal.
- Air ($d$) resistance is usually much smaller than friction for a toy - car on the floor. Friction ($c$) acts between the car's wheels (or body, if it's sliding) and the floor. It opposes the motion of the car, converting its kinetic energy into heat (through frictional work), and eventually stops the car.
### Answer:
c) Friction

## 2. When balanced forces act on an object, the object will:
### Brief Explanations:
According to Newton's first law ($F = ma$), when $F_{net}=0$ (balanced forces), $a = 0$. An acceleration of $0$ means the object's velocity (which is a combination of speed and direction) does not change.
- Speed up ($a$) implies $a>0$ (unbalanced force in the direction of motion).
- Slow down ($b$) implies $a < 0$ (unbalanced force opposite to the direction of motion).
- Spin ($d$) would imply a rotational acceleration, which also requires an unbalanced torque (a type of unbalanced force - related concept for rotation).
### Answer:
c) Not change motion

## 3. When unbalanced forces act on an object, it will:
### Brief Explanations:
From Newton's second law ($F_{net}=ma$), if $F_{net}
eq0$, then $a
eq0$. An acceleration ($a
eq0$) means a change in the object's velocity (either in speed, direction, or both).
- Stay still ($a$) would require $a = 0$ ($F_{net}=0$).
- Float ($c$) is related to buoyancy (a force balance in a fluid, usually vertical) and not a general result of unbalanced forces.
- Disappear ($d$) is a physical impossibility not related to force - motion laws.
### Answer:
b) Change motion

# 5. Think and Explain
## 1. Newton’s First Law means that
### Brief Explanations:
Newton's first law states that an object at rest will remain at rest, and an object in motion will remain in motion with a constant velocity (in a straight line) unless acted upon by an unbalanced force. It emphasizes the concept of inertia (the property of an object to resist changes in its state of motion) and the role of unbalanced forces in changing an object's motion.
### Answer:
an object at rest stays at rest and an object in motion stays in motion (in a straight line at a constant speed) unless acted on by an unbalanced force

## 2. A real - life example of inertia is
### Brief Explanations:
When a car suddenly stops, the passengers tend to keep moving forward. This is because the passengers (initially in motion with the car) have inertia. Their bodies resist the change in motion (the stop of the car) and continue moving in the original direction of motion until acted on by a force (such as the seatbelt or the dashboard).
### Answer:
when a car stops suddenly, passengers lurch forward

## 3. When forces are balanced,
### Brief Explanations:
From Newton's first law ($F_{net}=ma$), if $F_{net}=0$ (balanced forces), then $a = 0$. An acceleration of $0$ means the object's velocity (speed and direction) does not change. So, the object either remains at rest (if it was initially at rest) or continues to move with a constant velocity (if it was initially in motion).
### Answer:
the object’s motion does not change (it stays at rest or moves at a constant velocity)

## 4. When forces are unbalanced,
### Brief Explanations:
According to Newton's second law ($F_{net}=ma$), if $F_{net}
eq0$ (unbalanced forces), then $a
eq0$. An acceleration ($a
eq0$) implies a change in the object's velocity. The velocity can change in speed (speed up or slow down) or in direction (if the force is perpendicular or at an angle to the initial velocity, causing a change in the direction of motion).
### Answer:
the object’s motion changes (it accelerates, decelerates, or changes direction)

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QUESTION IMAGE

Question

Explanation:

3. Identify the Forces

A book resting on a desk

Answer:

A ball rolling and slowing down